Journal Cover Journal of Ecology
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   ISSN (Print) 0022-0477 - ISSN (Online) 1365-2745
   Published by John Wiley and Sons Homepage  [1589 journals]
  • How disturbance and dispersal influence intraspecific structure
    • Authors: Ceridwen I. Fraser; Ian D. Davies, David Bryant, Jonathan M. Waters
      Abstract: Recent studies have suggested that spatial patterns of intraspecific diversity can be influenced by density-dependent processes, which can inhibit effective migration of new lineages to established populations. How mechanisms such as dispersal and disturbance influence these processes is, however, still poorly understood.We hypothesised that (1) species with leptokurtic dispersal (frequent on small scales but rare on larger scales) would show no spatial structure on small scales and strong structure on large scales, and (2) disturbance would influence the chance of genetic turnover in a population.We tested these hypotheses using empirical genetic (mtDNA) data from field observations of a model taxon (the buoyant, forest-forming kelp Durvillaea, which exhibits leptokurtic dispersal distribution), and by conducting simulation analyses.Our data supported the first hypothesis, with no spatial structure detected on fine (metres) scales despite evidence of strong structure on larger (tens to hundreds of kilometres) scales. The second hypothesis was also supported, with simulations showing that disturbance increased the rate at which structure developed, and reduced the time to fixation (monopolisation by a single lineage). The chance of any lineage reaching fixation was directly related to its initial proportion in the population, and this relationship was unaffected by changes in disturbance size or dispersal capacity. We conclude that, in the absence of selection, extirpation is typically a prerequisite for population-genetic “turnover”, with remnant (refugial) individuals otherwise outnumbering immigrants.Synthesis. Disturbance plays a critical role in releasing density-dependent blocks to colonisation, and thus enables lineage turnover within species. Our results indicate that although both disturbance size and dispersal capacity play important roles in the formation of spatial structure within species, unless a population is totally extirpated, establishment of genetic lineages from elsewhere (turnover) is unlikely even for species that can disperse well.Disturbance plays a critical role in releasing density-dependent blocks to colonisation, and thus enables lineage turnover within species. Our results indicate that although both disturbance size and dispersal capacity play important roles in the formation of spatial structure within species, unless a population is totally extirpated, establishment of genetic lineages from elsewhere (turnover) is unlikely even for species that can disperse well.
      PubDate: 2017-12-05T06:37:08.442865-05:
      DOI: 10.1111/1365-2745.12900
       
  • Snow Depth, Soil Temperature, and Plant-Herbivore Interactions Mediate
           Plant Response To Climate Change
    • Authors: Rebecca Sanders-DeMott; Risa McNellis, Maroua Jabouri, Pamela H. Templer
      Abstract: 1.Northern forest ecosystems are projected to experience warmer growing seasons, as well as winters with reduced snowpack depth and duration. Reduced snowpack will expose soils to cold winter air and lead to increased frequency of freeze-thaw cycles. The interactions between warmer soils in the growing season and colder soils in winter may have important implications for the phenology, productivity, and nutrient content of forest plants.2.We conducted an experiment at Hubbard Brook Experimental Forest, NH, USA to examine the effects of growing season warming, reduced depth and duration of winter snowpack, as well as increased frequency of soil freeze-thaw cycles on sugar maple (Acer saccharum) and red maple (Acer rubrum) saplings. We examined the direct effects of soil temperatures on plant root health, timing of leaf-out, foliar nitrogen, rates of photosynthesis, and growth, as well as the indirect effects of snowpack reduction on herbivory on plant stems.3.A smaller winter snowpack and increased frequency of soil freeze-thaw cycles in winter led to increased root damage and delayed leaf-out for maple saplings. Snowpack reduction decreased rates of stem herbivory in winter, indicating that alleviation of aboveground stem damage in winters with reduced snowpack may offset the root damage incurred from successive soil freeze-thaw cycles in winters with low snowpack.4.Synthesis. By examining the response of two dominant tree species to simulated climate change in both the growing season and winter, we find that plant responses are mediated through a combination of changes in soil temperature and plant-herbivore interactions that differentially affect above- and belowground plant components. These results highlight the feedbacks between trophic levels that shape forest function and demonstrate the need for considering climate change across seasons in global change experiments to determine how forest function may change in the future.This article is protected by copyright. All rights reserved.
      PubDate: 2017-12-05T02:00:28.617708-05:
      DOI: 10.1111/1365-2745.12912
       
  • Plant community composition but not plant traits determine the outcome of
           soil legacy effects on plants and insects
    • Authors: Robin Heinen; Martijn Sluijs, Arjen Biere, Jeffrey A. Harvey, T. Martijn Bezemer
      Abstract: Plants leave species-specific legacies in the soil they grow in that can represent changes in abiotic or biotic soil properties. It has been shown that such legacies can affect future plants that grow in the same soil (plant–soil feedback, PSF). Such processes have been studied in detail, but mostly on individual plants. Here, we study PSF effects at the community level and use a trait-based approach both in the conditioning phase and in the feedback phase to study how 12 individual soil legacies influence six plant communities that differ in root size.We tested if (1) grassland perennial species with large root systems would leave a stronger legacy than those with small root systems, (2) grass species would leave a more positive soil legacy than forbs, and (3) communities with large root systems would be more responsive than small-rooted communities. We also tested (4) whether a leaf-chewing herbivore and a phloem feeder were affected by soil legacy effects in a community framework.Our study shows that the six different plant communities that we used respond differently to soil legacies of 12 different plant species and their functional groups. Species with large root systems did not leave stronger legacies than species with small root systems, nor were communities with large root systems more responsive than communities with root systems.Moreover, we show that when communities are affected by soil legacies, these effects carry over to the chewing herbivore Mamestra brassicae (Lepidoptera: Noctuidae) through induced behavioural changes resulting in better performance of a chewing herbivore on forb-conditioned soils than on grass-conditioned soils, whereas performance of the phloem feeder Rhopalosiphum padi (Hemiptera: Aphididae) remained unaffected.Synthesis. The results of this study shed light on the variability of soil effects found in previous work on feedbacks in communities. Our study suggests that the composition of plant communities determines to a large part the response to soil legacies. Furthermore, the responses to soil legacies of herbivores feeding on the plant communities that we observed, suggests that in natural ecosystems, the vegetation history may also have an influence on contemporary herbivore assemblages. This opens up exciting new areas in plant–insect research and can have important implications for insect pest management.Root size did not, but plant species and their functional group did explain legacy effects on soil bacteria and fungi (1). Community root size did not influence responses to soil legacies, neither by plant communities (2), nor their associated herbivores. Caterpillars feeding on test plant communities were affected by species- and functional group-specific legacies, whereas an aphid remained unaffected (3).
      PubDate: 2017-12-04T06:10:40.656304-05:
      DOI: 10.1111/1365-2745.12907
       
  • Rare events of massive plant reproductive investment lead to long-term
           density-dependent reproductive success
    • Authors: Magdalena Żywiec; Mateusz Ledwoń, Jan Holeksa, Piotr Seget, Barbara Łopata, José Maria Fedriani
      Abstract: The level of reproductive investment and density- and distance-dependent (DDD) processes are major determinants of plant reproductive output. The reproductive investment of a plant population varies temporally, but whether and how DDD processes are affected by population-level reproductive investment is a puzzle.We used a spatially explicit approach in order to examine DDD effects on Sorbus aucuparia crop sizes for a continuous period of 16 years. Our special interest was to investigate whether and how DDD processes affect long-term individual plant reproductive success (PRS) and whether such processes vary between years of relatively high and low population-level reproductive investment, measured as fruit crop size.Our study revealed that DDD processes of fruit crop relate to population-level reproductive investment. In most years, including all years with low and most years with moderate reproductive investment, no positive or negative DDD was found for PRS. However, significant negative density-dependent effects were found during most years of high and some years of moderate reproductive investment. During these years, the individual reproductive success decreased with increasing density of conspecifics.The overall accumulated long-term negative density-dependent pattern of PRS was determined by few sporadic years of high reproductive investment, rather than by the most frequent years of low or moderate reproductive investment, when the DDD effects were usually weak.Synthesis. Our study highlights the ecological relevance of relatively infrequent processes which affect plant reproductive success, stressing thus the importance of long-term ecological research.Density-dependent processes are critical for plant reproductive success but are seldom investigated in long-term studies. Our 16-year study revealed that negative density-dependent pattern of plant reproductive success accumulated over the study period was determined by a few sporadic years of high reproductive investment rather than by the most frequent years of low reproductive investment.
      PubDate: 2017-12-04T06:05:48.84534-05:0
      DOI: 10.1111/1365-2745.12896
       
  • Scatterhoarders drive long- and short-term population dynamics of a
           nut-producing tree, while pre-dispersal seed predators and herbivores have
           little effect
    • Authors: Elise C. Elwood; Nathanael I. Lichti, Sara F. Fitzsimmons, Harmony J. Dalgleish
      Abstract: Both seed predators and herbivores can have profound effects on individual plant growth, reproduction and survival, but their population-level effects are less well understood. While most plants interact with a suite of seed predators and herbivores over their life cycle, few studies incorporate the effects of multiple interacting partners and multiple life stages on plant population growth.We constructed a matrix model using 6 years of data from a rare, seed-producing population of American chestnut (Castanea dentata). We combined field demographic data with published experimental results on the effects of pre-dispersal seed predators (weevils) and post-dispersal seed predators (scatter-hoarding vertebrates) and incorporated the effect of vertebrate herbivores estimated from the field data. We explored the impact of these three different animal interactions for short-term (transient) and long-term (asymptotic) tree population growth. In addition, we used the model to explore the conditions under which scatter hoarding would function as a mutualism.Seed predators had greater effect on both short- and long-term population growth than herbivores. Although weevil infestation can greatly reduce the probability of germination, pre-dispersal seed predators had smaller effects on both short- or long-term population growth than post-dispersal predators. The elasticities of weevil-related parameters were also small. The effect of browsers on both the short- and long-term population growth rate were the smallest of the effects studied. Post-dispersal seed predation affected population growth the most in the interactions studied. The probability of seed removal was among the largest elasticities, similar in magnitude to survival of large trees.Synthesis. Our results indicate that neither weevils nor the intensity of browse damage observed at our study site are likely to hinder tree regeneration or reintroduction, although both reduced population growth. Although researchers and forest managers often assume that seeds are unimportant for long-lived tree populations, our test of this assumption shows that scatterhoarders and other post-dispersal seed consumers can significantly limit natural regeneration. Forest management that alters scatterhoarder behaviour could have significant effects on tree population dynamics that are largely unexplored.Our results indicate that neither weevils nor the intensity of browse damage observed at our study site are likely to hinder tree regeneration or reintroduction, although both reduced population growth. Although researchers and forest managers often assume that seeds are unimportant for long-lived tree populations, our test of this assumption shows that scatterhoarders and other post-dispersal seed consumers can significantly limit natural regeneration. Forest management that alters scatterhoarder behaviour could have significant effects on tree population dynamics that are largely unexplored.
      PubDate: 2017-12-04T06:05:40.585237-05:
      DOI: 10.1111/1365-2745.12902
       
  • Biological Flora of the British Isles: Neottia cordata
    • Authors: Milan Kotilínek; Irina Tatarenko, Jana Jersáková
      Abstract: This account presents information on all aspects of the biology of Neottia cordata (L.) Rich. (Lesser Twayblade; Listera cordata (L.) R. Br.) that are relevant to an understanding of its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, reproductive characteristics, herbivores, history and conservation.Neottia cordata is an inconspicuous orchid, confined to humid heathlands and woodlands rich in bryophytes in the British Isles.Neottia cordata is a polycarpic, perennial herb with populations maintained predominantly by vegetative reproduction from root suckers. The main perennating organ is a short rhizome that produces two new internodes each year. The long adventitious roots are mainly colonized not only by mycorrhizal basidiomycetes from the Sebacinales (clade B, Serendipitaceae) but also by several other fungal groups.The species flowers from mid-April to August depending on latitude and altitude. The flowers possess a sensitive rostellum that releases a viscid fluid when touched, ensuring that the pollinia are glued to the pollinator. The flowers produce nectar and are pollinated mainly by fungus gnats (Mycetophilidae and Sciaridae). Between 60% and 80% of open flowers set fruits.Neottia cordata is classified as Least Concern in Great Britain. It is still locally abundant in north and west Scotland but has declined elsewhere, especially at lower altitudes, because of burning on grouse moors, drainage of swamps and cutting of wet forests. It is likely to have been under-recorded throughout its range, particularly in earlier surveys, due to its inconspicuousness.Neottia cordata is an inconspicuous orchid of moist, acidic, humic soils. In the British Isles, it occurs mainly in sites rich with mosses, such as moors and bogs, or damp woodlands. It has a circumpolar distribution including North America, Europe and Asia. It reproduces by seeds and vegetatively by root suckers. The major pollinators are fungus gnats. Neottia cordata is threatened mainly by drainage and destruction of wet habitats, and it is listed as Vulnerable or Near Threatened in most European Red lists.
      PubDate: 2017-11-30T05:56:36.218487-05:
      DOI: 10.1111/1365-2745.12895
       
  • The role of bryophytes for tree seedling responses to winter climate
           change: Implications for the stress gradient hypothesis
    • Authors: Signe Lett; David A. Wardle, Marie-Charlotte Nilsson, Laurenz M. Teuber, Ellen Dorrepaal
      Abstract: When tree seedlings establish beyond the current tree line due to climate warming, they encounter existing vegetation, such as bryophytes that often dominate in arctic and alpine tundra. The stress gradient hypothesis (SGH) predicts that plant interactions in tundra become increasingly negative as climate warms and conditions become less harsh. However, for seedlings, climate warming might not result in lower winter stress, if insulating snow cover is reduced.We aimed to understand if bryophytes facilitate seedling survival in a changing winter climate and if these effects of bryophytes on tree seedlings comply with the SGH along elevational gradients under contrasting snow conditions.In the Swedish subarctic, we transplanted intact bryophyte cores covered by each of three bryophyte species and bryophyte-free control soil from above the tree line to two field common garden sites, representing current and future tree line air temperature conditions (i.e. current tree line elevation and a lower, warmer, elevation below the tree line). We planted seedlings of Betula pubescens and Pinus sylvestris into these cores and subjected them to experimental manipulation of snow cover during one winter.In agreement with the SGH, milder conditions caused by increased snow cover enhanced the generally negative or neutral effects of bryophytes on seedlings immediately after winter. Furthermore, survival of P. sylvestris seedlings after one full year was higher at lower elevation, especially when snow cover was thinner. However, in contrast with the SGH, impacts of bryophytes on over-winter survival of seedlings did not differ between elevations, and impacts on survival of B. pubescens seedlings after 1 year was more negative at lower elevation. Bryophyte species differed in their effect on seedling survival after winter, but these differences were not related to their insulating capacity.Synthesis. Our study demonstrates that interactions from bryophytes can modify the impacts of winter climate change on tree seedlings, and vice versa. These responses do not always comply with SGH, but could ultimately have consequences for large-scale ecological processes such as tree line shifts. These new insights need to be taken into account in predictions of plant species responses to climate change.Our study demonstrates that interactions from bryophytes can modify the impacts of winter climate change on tree seedlings, and vice versa. These responses do not always comply with SGH, but could ultimately have consequences for large-scale ecological processes such as tree line shifts. These new insights need to be taken into account in predictions of plant species responses to climate change.
      PubDate: 2017-11-30T05:55:58.50881-05:0
      DOI: 10.1111/1365-2745.12898
       
  • Patterns and drivers of biodiversity–stability relationships under
           climate extremes
    • Authors: Hans J. De Boeck; Juliette M. G. Bloor, Juergen Kreyling, Johannes C. G. Ransijn, Ivan Nijs, Anke Jentsch, Michaela Zeiter
      Abstract: Interactions between biodiversity loss and climate change present significant challenges for research, policy and management of ecosystems. Evidence suggests that high species diversity tends to increase plant community stability under interannual climate fluctuations and mild dry and wet events, but the overall pattern of diversity–stability relationships under climate extremes is unclear.We comprehensively review results from observational and experimental studies to assess the importance of diversity effects for ecosystem function under climate extremes. Both the broad literature review and a meta-analysis focused on the effects of extreme precipitation events on above-ground biomass reveal no significant interaction between species richness and climate extremes.Causes for variation in diversity effects under climate extremes are explored, from stress thresholds to biotic interactions and community assembly, and we consider how these may modulate the outcomes of biodiversity–stability relationships. We also examine how specific characteristics of climate extremes and timing of measurements may interact with mechanisms of diversity–stability relationships.Synthesis. Hypotheses tailored to the complexity of diversity effects, the implementation of standardised experiments and the use of trait-based biodiversity measures rather than species richness should lead to better causal understanding of whether and how biodiversity may protect ecosystems from adverse effects of climate extremes.We comprehensively review results from observational and experimental studies to assess the importance of biodiversity effects for ecosystem function under climate extremes and find no significant interaction between species richness and extremes. Causes for the observed variation in effects are explored, and suggestions are made to improve causal understanding of whether and how biodiversity may protect ecosystems from adverse climate extreme effects.
      PubDate: 2017-11-28T19:00:02.69993-05:0
      DOI: 10.1111/1365-2745.12897
       
  • Effects of light and topography on regeneration and coexistence of
           evergreen and deciduous tree species in a Chinese subtropical forest
    • Authors: Yi Jin; Sabrina E. Russo, Mingjian Yu
      Abstract: 1.Evergreen broad-leaved forests are widely distributed in eastern Asia with evergreen (EBL) and deciduous (DBL) broad-leaved tree species coexisting under the same climatic regime, raising questions as to the underlying mechanisms. Since EBL and DBL species differ in leaf lifespan, a key component of resource economic strategies, their coexistence might be attributed to regeneration niche partitioning across habitats varying in resource supply.2.We investigated the effects of variation in insolation and topography on regeneration of EBL and DBL species in a subtropical evergreen broad-leaved forest of eastern China after an ice storm that caused severe canopy disturbance.3.Using a mixed-effects modeling framework and census data from 2011 to 2014 on 8548 wild seedlings of 123 species, we quantified habitat preferences of EBL and DBL species during post-disturbance regeneration and how their survival and height relative growth rates varied among habitats.4.The relative density of DBL seedlings (proportional to all seedlings) was greater in habitats with greater (canopy gaps) compared to lesser (understory) insolation and increased with canopy gap size. However, DBL seedlings were not more frequent in higher (valleys) compared to lower (ridges) fertility habitats. Although DBL seedlings exhibited larger differences in growth between higher and lower resource habitats than EBL seedlings, their growth rates did not increase with canopy gap size. Seedlings of EBL species had high survival in all habitats, but larger DBL seedlings survived equally well on ridges. Consequently, the relative density of DBL seedlings declined in valleys, so that by 2014 it became more similar in valley and ridge habitats, whereas it remained higher in gaps than in the understory, and especially in larger gaps.5.Synthesis. Specialization on contrasting topographic habitats is considered the primary mechanism mediating coexistence between DBL and EBL species. Our results, however, suggest this may not always be true, since seedlings of DBL and EBL species partitioned regeneration niches based on light more so than topography. We propose that coexistence of DBL and EBL species can strongly depend upon canopy disturbance to create a mosaic of habitat patches, including high light gaps favoring regeneration of DBL species.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-28T09:40:22.921206-05:
      DOI: 10.1111/1365-2745.12911
       
  • Cereal progenitors differ in stand harvest characteristics from related
           wild grasses
    • Authors: Catherine Preece; Natalie F. Clamp, Gemma Warham, Michael Charles, Mark Rees, Glynis Jones, Colin P. Osborne
      Abstract: The domestication of crops in the Fertile Crescent began approximately 10,000 years ago indicating a change from a hunter-gatherer lifestyle to a sedentary, agriculture-based existence. The exploitation of wild plants changed during this transition, such that a small number of crops were domesticated from the broader range of species gathered from the wild. However, the reasons for this change are unclear.Previous studies have shown unexpectedly that crop progenitors are not consistently higher yielding than related wild grass species, when growing without competition. In this study, we replicate more closely natural competition within wild stands, using two greenhouse experiments to investigate whether cereal progenitors exhibit a greater seed yield per unit area than related wild species that were not domesticated.Stands of cereal progenitors do not provide a greater total seed yield per unit ground area than related wild species, but these crop progenitors do have greater reproductive efficiency than closely related wild species, with nearly twice the harvest index (the ratio of harvested seeds to total shoot dry mass).These differences arise because the progenitors have greater seed yield per tiller than closely related wild species, due to larger individual seed size but no reduction in seed number per tiller. The harvest characteristics of cereal progenitors may have made them a more attractive prospect than closely related wild species for the early cultivators who first planted these species, or could suggest an ecological filtering mechanism.Synthesis. Overall, we show that the maintenance of a high harvest index under competition, the packaging of seed in large tillers, and large seeds, consistently distinguish crop progenitors from closely related wild grass species. However, the archaeological significance of these findings remains unclear, since a number of more distantly related species, including wild oats, have an equally high or higher harvest index and yield than some of the progenitor species. Domestication of the earliest cereal crops from the pool of wild species available cannot therefore be explained solely by species differences in yield and harvest characteristics, and must also consider other plant traits.Crop progenitors differ from related wild grasses by the maintenance of high harvest index under competition, and having large tillers and seed size. However, the archaeological significance of these findings is unclear, as some wild species have an equally high or higher harvest index and yield than some progenitors. Early cereal domestication must therefore also consider other plant traits apart from harvest characteristics.
      PubDate: 2017-11-27T07:00:36.491357-05:
      DOI: 10.1111/1365-2745.12905
       
  • Corrigendum
    • PubDate: 2017-11-27T07:00:27.011359-05:
      DOI: 10.1111/1365-2745.12906
       
  • Scale dependence of the diversity–stability relationship in a
           temperate grassland
    • Authors: Yunhai Zhang; Nianpeng He, Michel Loreau, Qingmin Pan, Xingguo Han
      Abstract: A positive relationship between biodiversity and ecosystem stability has been reported in many ecosystems; however, it has yet to be determined whether and how spatial scale affects this relationship. Here, for the first time, we assessed the effects of alpha, beta and gamma diversity on ecosystem stability and the scale dependence of the slope of the diversity–stability relationship.By employing a long-term (33 years) dataset from a temperate grassland, northern China, we calculated the all possible spatial scales with the complete combination from the basic 1-m2 plots.Species richness was positively associated with ecosystem stability through species asynchrony and overyielding at all spatial scales (1, 2, 3, 4 and 5 m2). Both alpha and beta diversity were positively associated with gamma stability.Moreover, the slope of the diversity–area relationship was significantly higher than that of the stability–area relationship, resulting in a decline of the slope of the diversity–stability relationship with increasing area.Synthesis. With the positive species diversity effect on ecosystem stability from small to large spatial scales, our findings demonstrate the need to maintain a high biodiversity and biotic heterogeneity as insurance against the risks incurred by ecosystems in the face of global environmental changes.Based on (1) the positive diversity-stability relationships at all spatial scales, and alpha and beta diversity were positively associated with gamma stability, and (2) although the slope of the diversity-stability relationship with increasing area declined, species richness was positively associated with the magnitude of the diversity–stability relationship across areas, maintaining a high biodiversity and biotic heterogeneity is needed.
      PubDate: 2017-11-23T08:55:41.482198-05:
      DOI: 10.1111/1365-2745.12903
       
  • Nitrogen fertilization, not water addition, alters plant phylogenetic
           community structure in a semi-arid steppe
    • Authors: Xian Yang; Zhongling Yang, Jiaqi Tan, Guoyong Li, Shiqiang Wan, Lin Jiang
      Abstract: Anthropogenic environmental changes, such as nitrogen (N) enrichment and alteration in precipitation regimes, significantly influence ecosystems world-wide. However, we know little about whether and how these changes alter the phylogenetic properties of ecological communities.Based on a 7-year field experiment in the temperate semi-arid steppe of Inner Mongolia, China, we investigated the influence of increased N and precipitation on plant phylogenetic structure and phylogenetic patterns of species colonization and extinction.Our study demonstrated that N and water addition influenced different aspects of plant community structure. Water addition increased plant species richness by preventing species extinction and facilitating species colonization, without altering community phylogenetic structure. In contrast, N addition did not alter species richness, but promoted the colonization of species distantly related to the residents, changing community phylogenetic structure from being neutral to overdispersion. We also found evidence for abundance-based extinction where rarer species were at greater risk of extinction, and functional trait-based species extinction where shorter statured plants and shallower rooted plants were at greater risk of extinction.Synthesis. Our study provides the first experimental evidence that plant phylogenetic community structure responds differently to different aspects of global changes. Importantly, the colonization of non-resident species, rather than the extinction of resident species, contributed predominantly to changes in plant community phylogenetic structure in response to N amendment. Our findings highlight the importance of considering species phylogenetic relationships for a more complete understanding of anthropogenic influences on ecological communities.The reported study, conducted in the temperate semi-arid steppe in Inner Mongolia, China, examined how nitrogen and water addition influences plant phylogenetic community structure. Water addition did not alter community phylogenetic structure, whereas nitrogen addition transformed communities from phylogenetically neutral to overdispersion. The latter result was driven by the colonization of species distantly related to resident species under nitrogen enrichment.
      PubDate: 2017-11-23T08:55:26.979713-05:
      DOI: 10.1111/1365-2745.12893
       
  • Stand-level drivers most important in determining boreal forest response
           to climate change
    • Authors: Yan Boulanger; Anthony R. Taylor, David T. Price, Dominic Cyr, Guillaume Sainte-Marie
      Abstract: Forest ecosystems contain several climate-sensitive drivers that respond differentially to changes in climate and climate variability. For example, growth and regeneration processes are “stand-scale” drivers, while natural disturbances operate at “landscape scale”. The relative contributions of these different scale drivers of change in ecosystems create great uncertainty when simulating potential responses of a forest to changes in climate.Here, we assess those contributions, along with harvesting effects, on biomass (both total and of individual species) in the southern boreal forest of Canada under three climate scenarios (RCP 2.6, RCP 4.5 and RCP 8.5).Projections were performed for three future 30-year time periods, in four study regions located on an east–west transect, using a forest landscape model (LANDIS-II), parameterized using a forest patch model (PICUS). Projected future impacts were assessed for each driver of change, and found to vary greatly among regions, species, future period and forcing scenarios. Fire, and stand-scale climate-induced impacts, had the strongest effects on forest vegetation, as well as on total and species’ biomass under most RCP scenarios, but the largest impacts occurred mostly after 2050, particularly with the RCP 8.5 scenario.The relative importance and trends in species-specific impacts varied, both spatially and according to the different RCP scenarios. Western regions were generally more sensitive to stand-scale climate-induced changes, whereas eastern regions were more sensitive to changes in fire regime. Our study also highlights the importance of considering the prevalence of species-level functional traits when assessing the sensitivity of forest landscapes to a given driver of change in the context of increasing anthropogenic climate forcing.Synthesis. Increases in fire activity, and direct impacts of climate change on forest growth and regeneration, will be the most important drivers of future changes in southern boreal forest landscapes.Increases in fire activity, and direct impacts of climate change on forest growth and regeneration, will be the most important drivers of future changes in southern boreal forest landscapes.
      PubDate: 2017-11-22T04:20:46.41867-05:0
      DOI: 10.1111/1365-2745.12892
       
  • Pleiotropic effect of the Flowering Locus C on plant resistance and
           defence against insect herbivores
    • Authors: Sergio Rasmann; Julia Sánchez Vilas, Gaétan Glauser, Maria Cartolano, Janne Lempe, Miltos Tsiantis, John R. Pannell
      Abstract: Plants vary widely in the extent to which they defend themselves against herbivores. Because the resources available to plants are often site-specific, variation among sites dictates investment into defence and may reveal a growth–defence trade-off. Moreover, plants that have evolved different life-history strategies in different environments may situate themselves on this trade-off curve differently. For instance, plants that flower later have a longer vegetative life span and may accordingly defend themselves differently than those that flower earlier.Here, we tested whether late-flowering plants, with a longer vegetative life span, invest more in defence than early-flowering plants, using recombinant genotypes of the annual herb Cardamine hirsuta that differ in flowering time as a result of differences in the activity of the major floral repressor Flowering Locus C (FLC).We found that variation at FLC was mainly responsible for regulating flowering time and allocation to reproduction, but this partially depended on where the plants grew. We also found that variation at FLC mediated plant allocation to defence, with late-flowering plants producing higher levels of total glucosinolates and stress-related phytohormones. Nonetheless, plant growth and the qualitative values of plant defence and plant resistance against specialist herbivores were mainly independent from FLC.Synthesis. Our results highlight pleiotropic effects associated with flowering-time genes that might influence plant defence and plant–herbivore interactions.This study investigates the effect of variation in the Flowering Locus C (FLC), a major regulator of flowering, on plant growth, plant defence and resistance against herbivores. We used recombinant genotypes—differing in the activity of FLC of Cardamine hirsuta that were grown in the Swiss Alps at different altitudes and subsequently exposed to a specialist herbivore. We found that while variation at FLC did not affect plant growth, insect growth rate or the qualitative values of plant defence, it did affect plant allocation to reproduction and defences, with late-flowering plants producing higher levels of total glucosinolates and stress-related phytohormones.
      PubDate: 2017-11-20T06:58:37.120897-05:
      DOI: 10.1111/1365-2745.12894
       
  • Spatial patterns of local species richness reveal importance of frugivores
           for tropical forest diversity
    • Authors: Wirong Chanthorn; Thorsten Wiegand, Stephan Getzin, Warren Y. Brockelman, Anuttara Nathalang
      Abstract: Seed dispersal by frugivores, particularly primates, plays an important role in structuring and maintaining tree diversity in tropical forests. However, little is known about the effect of frugivores on the diversity of saplings and large trees.We used detailed census data from the fully mapped 30-ha Mo Singto forest dynamics plot in Thailand together with spatial point pattern analysis to find out if the local species richness of small (dbh
      PubDate: 2017-11-20T06:55:48.798136-05:
      DOI: 10.1111/1365-2745.12886
       
  • Land use in mountain grasslands alters drought response and recovery of
           carbon allocation and plant-microbial interactions
    • Authors: Stefan Karlowsky; Angela Augusti, Johannes Ingrisch, Roland Hasibeder, Markus Lange, Sandra Lavorel, Michael Bahn, Gerd Gleixner
      Abstract: 1.Mountain grasslands have recently been exposed to substantial changes in land-use and climate and in the near future will likely face an increased frequency of extreme droughts. To date is not known how the drought responses of carbon (C) allocation, a key process in the C cycle, are affected by land-use changes in mountain grassland.2.We performed an experimental summer drought on an abandoned grassland and a traditionally managed hay meadow and traced the fate of recent assimilates through the plant-soil continuum. We applied two 13CO2 pulses, at peak drought and in the recovery phase shortly after rewetting.3.Drought decreased total C uptake in both grassland types and led to a loss of aboveground carbohydrate storage pools. The belowground C allocation to root sucrose was enhanced by drought, especially in the meadow, which also held larger root carbohydrate storage pools.4.The microbial community of the abandoned grassland comprised more saprotrophic fungal and Gram (+) bacterial markers compared to the meadow. Drought increased the newly introduced AM and saprotrophic (A+S) fungi:bacteria ratio in both grassland types. At peak drought the 13C transfer into AM fungi, saprotrophic fungi and Gram (-) bacteria was more strongly reduced in the meadow than in the abandoned grassland, which contrasted the patterns of the root carbohydrate pools.5.In both grassland types the C allocation largely recovered after rewetting. Slowest recovery was found for AM fungi and their 13C uptake. In contrast, all bacterial markers quickly recovered C uptake. In the meadow, where plant nitrate uptake was enhanced after drought, C uptake was even higher than in control plots.6.Synthesis. Our results suggest that resistance and resilience (i.e. recovery) of plant C dynamics and plant-microbial interactions are negatively related, i.e. high resistance is followed by slow recovery and vice versa. The abandoned grassland was more resistant to drought than the meadow and possibly had a stronger link to AM fungi that could have provided better access to water through the hyphal network. In contrast, meadow communities strongly reduced C allocation to storage and C transfer to the microbial community in the drought phase, but in the recovery phase invested C resources in the bacterial communities to gain more nutrients for regrowth. We conclude that management of mountain grasslands increases their resilience to drought.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T04:06:10.686897-05:
      DOI: 10.1111/1365-2745.12910
       
  • Domesticated honeybees facilitate interspecific hybridization between two
           Taraxacum congeners
    • Authors: Youhong Peng; Yuran Dong, Haigen Xu, Xinqiang Xi, Karl J. Niklas, Shucun Sun
      Abstract: 1.Interspecific hybridization is common in plants under natural conditions, but the ecological mechanisms underlying when and how it happens have not fully been understood.2.Taraxacum calanthodium and T. lugubre are two herbaceous annals co-occurring in alpine meadows of the eastern Tibetan Plateau that share the same pollinators including domestic honeybees during their overlapping flowering times. Because honeybees tend to visit flowers less discriminatively when bee densities are high, we hypothesized that intense apiculture would facilitate hybridization between these two congeneric species.3.We tested this hypothesis by examining the frequencies of the two parent species occurrence and the hybrid (based on morphological and genetic differences) along three transects radiating from well-established apiaries.4.Experiments show that both Taraxacum calanthodium and T. lugubre produce seeds sexually and asexually, and that they can hybridize via pollen transfer. Bee visitation rates and the frequency of the hybrid were significantly higher in the sites nearest to apiaries compared to distant site along each of the three transects. The hybrids were consistently genetically intermediate between the two species, as indicated by Simple Sequence Repeat-based analyses.5.Synthesis. These data indicate that domestic honeybees foster interspecific hybridization between the two Taraxacum species and that anthropogenic effects on pollen vectors can significantly influence species hybridization in nature. We suggest that more effort should be made to quantify the effects of environmental change on pollinators and their effects on species evolution.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T04:00:21.187878-05:
      DOI: 10.1111/1365-2745.12909
       
  • The dynamics of Kelp Forests in the Northeast Pacific Ocean and the
           relationship with environmental drivers
    • Authors: Catherine A. Pfister; Helen D. Berry, Thomas Mumford
      Abstract: 1.The dynamics of foundation species in ecosystems are key to the fate of many species. Kelp forests are foundation species in temperate ocean ecosystems and contribute to carbon storage, macronutrient dynamics, primary production, and biodiversity of myriad associated species. Downward trends in their abundance globally have been of concern.2.We analyzed 26 years of aerial censuses (1989-2015) of 2 canopy kelp species in Washington State (USA) waters. We compared these modern censuses with censuses in 1911 and 1912 to determine the persistence of kelp cover over the past century. Using Auto-regressive Integrated Moving Average (ARIMA) models, we compared kelp dynamics with likely environmental drivers, including local environmental variables and ocean indices for this region.3.Kelp remains at historic levels in many areas, though some eastern populations in proximity to greater human populations are the exception to this pattern. Over the last 26 years, kelp abundance showed high spatial autocorrelation in western areas of Straits of Juan de Fuca, with more variable populations in the annual species and eastward toward Puget Sound. Both species covaried positively in their abundance throughout most of the study area, suggesting environmental factors rather than competition, drove their dynamics. The population dynamics of these kelp species showed that the abundance one year previous was an important predictor, and cyclic dynamics were not indicated using Auto-regressive Integrated Moving Average (ARIMA) models. Kelp abundance correlated inversely with the Pacific Decadal Oscillation and the Oceanic Nino Index, and positively with the North Pacific Gyre Oscillation, indicating that large-scale processes associated with colder seawater temperatures were associated with greater relative abundance of kelp.4.Synthesis. Kelp beds in the northern California Current Large Marine Ecosystem have mostly remained persistent over the past century and over many km, but some areas may have decreased in abundance. The sensitivity of these populations to indices of ocean climate, our demonstration that a historic 93-year SST record (Race Rocks, Canada) showed a 0.72°C increase, and the classification of some areas as high variability-low abundance, suggest that the viability of these foundational species remain a concern into the future.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-14T03:55:37.402987-05:
      DOI: 10.1111/1365-2745.12908
       
  • Why we do not expect dispersal probability density functions based on a
           single mechanism to fit real seed shadows
    • Authors: Roger D. Cousens; Barry D. Hughes, Mohsen B. Mesgaran
      Abstract: Bullock et al. (Journal of Ecology 105:6-19, 2017) have suggested that the theory behind the Wald Analytical Long Distance (WALD) model for wind dispersal from a point source needs to be re-examined. This is on the basis that an inverse Gaussian probability density function (pdf) does not provide the best fit to seed shadows around individual source plants known to be dispersed by wind.We present two reasons why we would not necessarily expect any of the standard mechanistically derived pdfs to fit real seed shadows any better than empirical functions.Firstly, the derivation of “off-the-shelf” pdfs such as the Gaussian, exponential and inverse Gaussian involves only one of the processes and factors that together generate a real seed shadow. It is implausible to expect that a single-process model, no matter how sophisticated in detail, will capture the behaviour of an entire, complex system, which may involve a number of sequential random processes, or a superposition of parallel random processes, or both.Secondly, even if there is only one process involved and we have a perfect model for that process, the basic parameters of the model would be difficult to pin down precisely. Moreover, these parameters are unlikely to remain constant over a dispersal season, so that effectively we observe the outcome of a linear combination of dispersal events with different parameter values, constituting a form of averaging over the parameters of the distribution. Simple examples show that averaging a pdf over its parameters can lead to a pdf from an entirely different class.Synthesis. The failure of the inverse Gaussian model to fit seed shadow data is not in itself a reason to doubt the validity of the Wald Analytical Long Distance model for movement of particles through the air under specified environmental conditions. A greater awareness is needed of the differences between the Wald Analytical Long Distance and the inverse Gaussian (or Wald) and the purposes for which they are used. The complexity of dispersing populations of seeds means that any of the standard mechanistically derived pdfs will actually be merely empirical in this context. Shape and flexibility of a pdf is far more important for adequately describing data than some perceived higher status.The failure of the inverse Gaussian model to fit seed shadow data is not in itself a reason to doubt the validity of the Wald Analytical Long Distance model for movement of particles through the air under specified environmental conditions. A greater awareness is needed of the differences between the Wald Analytical Long Distance and the inverse Gaussian (or Wald Analytical Long Distance) and the purposes for which they are used. The complexity of dispersing populations of seeds means that any of the standard mechanistically derived pdfs will actually be merely empirical in this context. Shape and flexibility of a pdf is far more important for adequately describing data than some perceived higher status.
      PubDate: 2017-11-13T06:15:19.437868-05:
      DOI: 10.1111/1365-2745.12891
       
  • Herbaceous competition and browsing may induce arrested succession in
           central European forests
    • Authors: Timothy Thrippleton; Harald Bugmann, Rebecca S. Snell
      Abstract: Arrested succession, that is, an ecosystem permanently halted in an early successional, typically non-forested state, has been suggested to result from intense competition by understorey vegetation, high browsing pressure and additional disturbances, but the relative importance of these factors is unclear. In addition, distinguishing between permanently arrested succession or merely delayed succession may be highly challenging, if not impossible, due to the large time-scales involved.We used the dynamic vegetation model LandClim to systematically explore the effect of multiple factors on delayed and arrested succession over a time span of 1,000 years, starting from an unforested state. We included abiotic and biotic factors as well as large-scale overstorey disturbance, in four Central European landscapes.Arrested succession occurred in 1%–14% of the simulations. Among the non-arrested simulations, 95% reached a forested state (defined as ≥10% canopy cover) within 100 years. Large herbaceous biomass was the most important predictor for arrested succession, followed by browsing and large-scale disturbances. Combinations of factors were important at particular locations in the landscape, where understorey competition and browsing jointly induced a strong establishment filter. Abiotic conditions consistently influenced the probability of arrested succession, with a low probability under mesic conditions and increased likelihood in more xeric parts of the landscapes.Synthesis. We demonstrated that permanently arrested succession has the potential to occur in temperate forests, particularly under a combination of high amounts of herbaceous biomass and ungulate browsing in drought-constrained landscape positions. We thus conclude that considering environmental heterogeneity at the landscape scale is key for understanding the conditions that lead to delayed and arrested succession.We demonstrate that permanently arrested succession has the potential to occur in temperate forests, particularly under a combination of high amounts of herbaceous biomass and ungulate browsing in drought-constrained landscape positions. We thus conclude that considering environmental heterogeneity at the landscape scale is key for understanding the conditions that lead to delayed and arrested succession.
      PubDate: 2017-11-13T05:38:45.824243-05:
      DOI: 10.1111/1365-2745.12889
       
  • All dispersal functions are wrong, but many are useful: A response to
           Cousens et al.
    • Authors: James M. Bullock; Danny A. P. Hooftman, Riin Tamme, Lars Götzenberger, Meelis Pärtel, Laura Mallada González, Steven M. White
      Abstract: To address the lack of information about the shape and extent of real dispersal kernels, Bullock et al. (Journal of Ecology 105:6-19, 2017) synthesised empirical information on seed dispersal distances. Testing the fit of a variety of probability density functions, they found no function was the best-fitting for all datasets but some outperformed others. Cousens et al. (Journal of Ecology, 2017) focus on the specific finding of the generally poor fit of the WALD function to wind dispersal data and use this to argue that mechanistically derived functions would not be expected to fit data particularly well.We agree in part with this argument and discuss the issues that may lead to poor fit, including the simplifying assumptions of the WALD and the complexity of the dispersal process. We explain the fundamental linkage between the mechanistic form of the WALD and the derived function used for fitting to data.We demonstrate, however, that the logic that a mechanistically based function could fit to data is valid, under the hypothesis that it encompasses the key processes determining the dispersal kernel. This argument is supported by the facts that: (1) our analyses and others have shown the WALD performs well in a number of cases; and (2) the WALD is the best-fitting function for an example in which we simulate dispersal data using a realistic representation of variability in the wind dispersal process.Synthesis. While there are reasons that mechanistically derived functions may not fit well to empirical data, they do in some empirical and simulated cases and this suggests they can capture the dispersal behaviour of real systems. Mechanistic functions should be explored along with other more general functions when describing empirical data to investigate their simplifying assumptions and to add to our arsenal of functions for analysing dispersal data. Analyses using these functions are critical if we are to move from simply describing the system in which the data were gathered to gaining more general insights into dispersal and predicting its consequences.While there are reasons that mechanistically derived functions may not fit well to empirical data, they do in some empirical and simulated cases and this suggests they can capture the dispersal behaviour of real systems. Mechanistic functions should be explored along with other more general functions when describing empirical data to investigate their simplifying assumptions and to add to our arsenal of functions for analysing dispersal data. Analyses using these functions are critical if we are to move from simply describing the system in which the data were gathered to gaining more general insights into dispersal and predicting its consequences.
      PubDate: 2017-11-13T05:38:19.55542-05:0
      DOI: 10.1111/1365-2745.12890
       
  • Manipulating the system: How large herbivores control bottom-up regulation
           of grasslands
    • Authors: Douglas A. Frank; Rick L. Wallen, E. William Hamilton, Patrick J. White, Jason D. Fridley
      Abstract: Decades of grazing studies have identified a number of key plant and soil processes affected by large herbivores and how those grazer effects vary among different grassland types. However, there remains little mechanistic understanding about how the effects of grazers on plants and soils may be biogeochemically linked in regulating grassland processes.Here we measured monthly plant and soil variables, including soil moisture, soil nitrogen (N) availability, plant biomass, shoot N concentration and plant production, in grazed and ungrazed (fenced) grasslands during the 2012–2014 growing seasons. Measurements were used to assess direct and indirect biogeochemical pathways by which grazers influenced net above-ground plant production (NAP) in dry and mesic grasslands in Yellowstone National Park (YNP).Herbivores only had direct effects on plant variables at the dry grassland compared to direct and indirect effects on both plant and soil variables at the mesic grassland. By enhancing leaf N content at both grasslands, grazers shifted the resource controlling NAP from N in ungrazed grassland to moisture, and potentially phosphorus and/or other soil nutrients, in grazed grassland.Synthesis. These results indicate the mechanistic linkage between top-down (herbivore) and bottom-up (soil resource) control of grassland production. Changing the resources that limit net above-ground plant production (NAP) likely has a profound impact on how grazed vs. ungrazed Yellowstone National Park (YNP) grasslands respond to environmental (e.g., climate, atmospheric N deposition) variability. Because grazing enhances leaf N among many types of grasslands, increasing the sensitivity of plant production to the availability of moisture and nutrients other than N may be a general response of grasslands to grazing.By enhancing leaf nitrogen content, Yellowstone grazers shift the resource controlling plant production from nitrogen in ungrazed grassland to moisture in grazed grassland. Changing resources that regulate plant production likely has profound effects on how grazed vs. ungrazed YNP grasslands respond to environmental (e.g., climate, atmospheric nitrogen deposition) variability.
      PubDate: 2017-11-09T04:50:40.825784-05:
      DOI: 10.1111/1365-2745.12884
       
  • A 37-year experimental study of the effects of structural alterations on a
           shrub community in the Mojave Desert, California
    • Authors: Bruce E. Mahall; Paul J. Fonteyn, Ragan M. Callaway, William H. Schlesinger
      Abstract: 1.In 1977 an experiment was initiated in the Mojave Desert to investigate the relationship between shrub interactions and structure in a community dominated by Ambrosia dumosa and Larrea tridentata. Here, as in much of the Mojave, Larrea were regularly distributed, Ambrosia occurred in aggregations, and the two were randomly distributed relative to each other. Pre-dawn xylem pressure potentials (PDXPPs) of single Ambrosia or Larrea in centers of 100m2 circular plots were monitored to assess effects of intraspecific, interspecific, and total removals of neighboring shrubs. Contrary to theory, results over the next two years indicated interspecific interference was more intense than intraspecific interference in both species.2.These plots were maintained through 2014. Measurements of seedling recruitment from 1980 to 2014, and of PDXPP, aboveground biomass, and canopy senescence from 2003 to 2014 were conducted.3.Recruitment of both species was substantial immediately after the removals, but declined to very low levels after 1983. Ambrosia recruited into all Ambrosia and Total-Removal plots, but Larrea recruited only into plots that contained mature Ambrosia.4.PDXPPs of monitored shrubs continued to be enhanced in removal plots for at least 27 years, but this changed from most being due to interspecific removals in both species to intraspecific removals causing most enhancement in Ambrosia and inter- and intraspecific removals causing nearly equal enhancements in Larrea.5.Aboveground biomasses of monitored Ambrosia and Larrea were 2.1X and 2.8X larger in Total-Removal plots, 1.6X and 1.7X larger in intraspecific removal plots, respectively, and 1.1X larger in interspecific removal plots for both species than those in Control plots, indicating the absence of intraspecific interference had the dominant long-term effect.6.Canopy senescence differed between Ambrosia and Larrea in extent, timing and effect of specific removal treatments; it was greatest for both species in Controls, averaging 75% and 34%, respectively.7.Synthesis. Shrub interactions and their relations to community structure are mechanistically and spatially complex. Differences between short-term and long-term responses to removals reveal multi-tiered, temporally dynamic feedback loops between shrub interactions and community structure driven by demographics, species-specific root growth, resource competition, communications, and territoriality.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-09T01:15:42.316417-05:
      DOI: 10.1111/1365-2745.12904
       
  • Poor plant performance under simulated climate change is linked to
           mycorrhizal responses in a semi-arid shrubland
    • Authors: Lupe León-Sánchez; Emilio Nicolás, Marta Goberna, Iván Prieto, Fernando T. Maestre, José Ignacio Querejeta
      Abstract: Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands world-wide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere–microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change.We conducted a 4-year manipulative study in a semi-arid shrubland in the Iberian Peninsula to assess the effects of warming (c. 2.5°C; W), rainfall reduction (c. 30%; RR) and their combination (W+RR) on the performance of native shrubs (Helianthemum squamatum) and their associated mycorrhizal fungi.Warming (W and W+RR) decreased the net photosynthetic rates of H. squamatum shrubs by c. 31% despite concurrent increases in stomatal conductance (c. 33%), leading to sharp decreases (c. 50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by c. 36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (c. 10%–20%) in photosynthesis, stomatal conductance and shoot growth.Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high-throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non-mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments.Synthesis. Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semi-arid shrublands, and point to the importance of a deeper understanding of plant–soil feedbacks to predict dryland vegetation responses to forecasted aridification. The interdependent responses of plants and ectomycorrhizal fungi to warming and rainfall reduction may lead to a detrimental feedback loop on vegetation productivity and nutrient pool size, which could amplify the adverse impacts of forecasted climate change on ecosystem functioning in EMF-dominated drylands.Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semi-arid shrublands, and point to the importance of a deeper understanding of plant–soil feedbacks to predict dryland vegetation responses to forecasted aridification. The interdependent responses of plants and ectomycorrhizal fungi to warming and rainfall reduction may lead to a detrimental feedback loop on vegetation productivity and nutrient pool size, which could amplify the adverse impacts of forecasted climate change on ecosystem functioning in EMF-dominated drylands.
      PubDate: 2017-11-08T06:21:03.861395-05:
      DOI: 10.1111/1365-2745.12888
       
  • Declining growth of deciduous shrubs in the warming climate of continental
           western Greenland
    • Authors: Cassandra M. Gamm; Patrick F. Sullivan, Agata Buchwal, Roman J. Dial, Amanda B. Young, David A. Watts, Sean M. P. Cahoon, Jeffrey M. Welker, Eric Post
      Abstract: Observational and experimental studies have generally shown that warming is associated with greater growth and abundance of deciduous shrubs in arctic ecosystems. It is uncertain, however, if this trend will persist in the future.Our study examined growth responses of deciduous shrubs to climate change over the late 20th and early 21st centuries near Kangerlussuaq in western Greenland. We combined shrub dendrochronology, stable isotope analysis and weekly measurements of leaf gas exchange to examine the drivers of secondary growth in two widespread and dominant deciduous shrub species: Salix glauca and Betula nana.Betula showed a dramatic growth decline beginning in the early 1990s, when correlations between growing season air temperature and growth shifted from neutral to strongly negative. Salix also showed a growth decline, but it began slightly later and was more pronounced among older stems. May–August mean air temperature of c. 7°C appeared to be an important threshold.Carbon isotope discrimination (∆13C) in α-cellulose of Salix growth rings declined strongly during the period of reduced growth, suggesting drought-induced stomatal closure as a possible cause. Leaf gas exchange of Salix was also highly sensitive to seasonal variation in moisture availability. Betula growth declined more dramatically than Salix, but leaf gas exchange was less sensitive to moisture availability and there was less evidence of a ∆13C trend. We hypothesize that the dramatic Betula growth decline might reflect the combined effects of increasing moisture limitation, repeated defoliation during recent moth outbreaks and greater browsing by a growing muskoxen population.Synthesis. Our findings contrast with widespread observations of increasing shrub growth in the Arctic and instead point to a potential decline in the flux of carbon into a pool with a long mean residence time (wood). While our study area is warmer and drier than much of the Arctic, our results may serve as an early indicator of potential effects of rising temperature in other arctic ecosystems.We combined physiological measurements with shrub dendrochronology to examine drivers of secondary growth in two dominant deciduous shrubs. We found growth declines in both species that were at least partially associated with moisture limitation. While our study area is relatively warm and dry, our results may serve as an early warning of potential climate change effects in other arctic ecosystems.
      PubDate: 2017-11-07T08:35:58.35054-05:0
      DOI: 10.1111/1365-2745.12882
       
  • Direct and indirect controls on organic matter decomposition in four
           coastal wetland communities along a landscape salinity gradient
    • Authors: Camille L. Stagg; Melissa M. Baustian, Carey L. Perry, Tim J.B. Carruthers, Courtney L. Hall
      Abstract: 1.Coastal wetlands store more carbon than most ecosystems globally. As sea level rises, changes in flooding and salinity will potentially impact ecological functions, such as organic matter decomposition, that influence carbon storage. However, little is known about the mechanisms that control organic matter loss in coastal wetlands at the landscape scale. As sea level rises, how will the shift from fresh to salt-tolerant plant communities impact organic matter decomposition' Do long-term, plant-mediated, effects of sea-level rise differ from direct effects of elevated salinity and flooding'2.We identified internal and external factors that regulated indirect and direct pathways of sea-level rise impacts, respectively, along a landscape-scale salinity gradient that incorporated changes in wetland type (fresh, oligohaline, mesohaline and polyhaline marshes). We found that indirect and direct impacts of sea-level rise had opposing effects on organic matter decomposition.3.Salinity had an indirect effect on litter decomposition that was mediated through litter quality. Despite significant variation in environmental conditions along the landscape gradient, the best predictors of above- and belowground litter decomposition were internal drivers, initial litter nitrogen content and initial litter lignin content, respectively. Litter decay constants were greatest in the oligohaline marsh and declined with increasing salinity, and the fraction of litter remaining (asymptote) was greatest in the mesohaline marsh. In contrast, direct effects of salinity and flooding were positive. External drivers, salinity and flooding, stimulated cellulytic activity, which was highest in the polyhaline marsh.4.Synthesis: Our results indicate that as sea level rises, initial direct effects of salinity will stimulate decay of labile carbon, but over time as plant communities shift from fresh to polyhaline marsh, litter decay will decline, yielding greater potential for long-term carbon storage. These findings highlight the importance of quantifying carbon loss at multiple temporal scales, not only in coastal wetlands, but also in other ecosystems where plant-mediated responses to climate change will have significant impacts on carbon cycling.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-07T05:01:12.347578-05:
      DOI: 10.1111/1365-2745.12901
       
  • Woodland resilience to regional drought: Dominant controls on tree
           regeneration following overstorey mortality
    • Authors: Miranda D. Redmond; Peter J. Weisberg, Neil S. Cobb, Michael J. Clifford
      Abstract: Drought events occurring under warmer temperatures (i.e. “hotter droughts”) have resulted in widespread tree mortality across the globe, and may result in biome-level vegetation shifts to alternate vegetation types if there is a failure of trees to regenerate. We investigated how overstorey trees, understorey vegetation, and local climatic and edaphic conditions interact to influence tree regeneration, a key prerequisite for resilience, in a region that has experienced severe overstorey tree mortality due to hotter droughts and beetle infestations.We used detailed field observations from 142 sites that spanned a broad range of environmental conditions to evaluate the effects of climate and recent tree mortality on tree regeneration dynamics in the spatially extensive piñon (Pinus edulis)-juniper (Juniperus osteosperma, Juniperus monosperma) woodland vegetation type of the southwestern USA. We used a structural equation modelling framework to identify how tree mortality and local climatic and edaphic conditions affect piñon and juniper regeneration and electivity analyses to quantify the species-specific associations of tree juveniles with overstorey trees and understorey shrubs.Piñon regeneration appears to be strongly dependent upon advanced regeneration, (i.e. the survival of juvenile trees that established prior to the mortality event), the survival of adult seed-bearing trees (inferred from basal area of surviving trees) and the facilitative effects of overstorey trees for providing favourable microsites for seedling establishment. Model results suggest that local edaphoclimatic conditions directly affected piñon and juniper regeneration, such that stands with hotter, drier local climatic conditions and lower soil available water capacity had limited tree regeneration following large-scale dieback.Synthesis. We identify four indicators of resilience to hotter drought conditions: (1) abundant advance regeneration of tree seedlings; (2) sufficient canopy cover for survival of emergent seedlings and existing regeneration; (3) sufficient seed source from surviving trees with high reproductive output; (4) areas with cooler and wetter local climates and greater soil available water capacity. In the absence of these conditions, there is greater likelihood of woodlands transitioning to more xeric vegetation types following dieback.We identify four indicators of resilience to hotter drought conditions: (1) abundant advance regeneration of tree seedlings; (2) sufficient canopy cover for survival of emergent seedlings and existing regeneration; (3) sufficient seed source from surviving trees with high reproductive output; (4) areas with cooler and wetter local climates and greater soil available water capacity. In the absence of these conditions, there is greater likelihood of woodlands transitioning to more xeric vegetation types following dieback.
      PubDate: 2017-11-06T19:00:02.658585-05:
      DOI: 10.1111/1365-2745.12880
       
  • Limited stand expansion by a long-lived conifer at a leading northern
           range edge, despite available habitat
    • Authors: John Krapek; Brian Buma
      Abstract: In an era of rapid climate change, understanding the natural capacity of species' ranges to track shifting climatic niches is a critical research and conservation need. Because species do not move across the landscape through empty space, but instead have to migrate through existing biotic communities, basic dispersal ecology and biotic interactions are important considerations beyond simple climate niche tracking.Yellow-cedar (Callitropsis nootkatensis), a long-lived conifer of the North Pacific coastal temperate rainforest region, is thought to be undergoing a continued natural range expansion in southeast Alaska. At the same time, yellow-cedar's trailing edge is approaching its leading edge in the region, due to climate-induced root injury leading to widespread mortality over the past century. To examine the current dispersal capacity of yellow-cedar at its leading range edge, and potential for the species' leading edge to stay ahead of its trailing edge, we characterized recent yellow-cedar stand development near Juneau, Alaska, and surveyed the spread of yellow-cedar seedlings just beyond existing stand boundaries.Despite suitable habitat beyond stand edges, stand expansion appears limited in recent decades to centuries. Large quantities of seed are germinating within stands and just beyond boundaries, but seedlings are not developing to maturity. Furthermore, c. 100–200-year-old yellow-cedar trees are located abruptly at stand boundaries, indicating stand expansion is in a period of stasis with a last pulse at the end of the Little Ice Age climate period.Vegetative regeneration is common across stands and may be an adaptive strategy for this long-lived tree to persist on the landscape until conditions are favourable for successful seedling recruitment, leading to an overall punctuated migration and colonization of new landscapes.Synthesis. Species ranges do not always respond linearly to shifting climatic conditions. Instead, successful colonization of new habitat may be tied to episodic, threshold-related landscape phenomena, dispersal ability, and competition with existing plant communities.Species ranges do not always respond linearly to shifting climatic conditions. Instead, successful colonization of new habitat may be tied to episodic, threshold-related landscape phenomena, dispersal ability, and competition with existing plant communities.
      PubDate: 2017-11-06T05:37:04.405393-05:
      DOI: 10.1111/1365-2745.12885
       
  • Simulated caribou browsing limits the effect of nutrient addition on the
           
    • Authors: Clara Morrissette-Boileau; Stéphane Boudreau, Jean-Pierre Tremblay, Steeve D. Côté
      Abstract: 1.Warmer summer temperatures and enhanced soil fertility increase shrub growth in tundra ecosystems, and these factors have likely contributed to shrub expansion at the circumpolar scale over the last decades. Conversely, large herbivores have the potential to counteract the positive impacts of climate change on shrub growth. Indeed, by stripping the leaves, herbivores have the potential to control the growth of shrub species and, consequently, limit their expansion.2.To disentangle the impacts of climate change and herbivory on Betula glandulosa Michx., we conducted a 5-yr factorial experiment near Deception Bay, Nunavik, Canada, in which we simulated warmer temperatures, increased nitrogen availability and three caribou browsing intensities during the growing season. At the end of the experiment, we harvested the aboveground biomass of B. glandulosa and conducted dendrochronological analyses on stems.3.Fertilized plots under ambient temperature had 34% greater shrub biomass than plots assigned to the combined treatment of nitrogen addition and warmer temperatures. Browsing intensity had no effect on final biomass. Nitrogen addition increased radial growth (18-33%; 3 years out of 5). Overall, browsing had a cumulative negative impact on B. glandulosa radial growth during the 5-yr experiment. While browsing had no effect in the first year of the experiment, moderate browsing (leaves stripped on 25% of available shoots) decreased radial growth by 27% at year 2, 32% at year 4 and 27% at year 5. Heavy browsing (leaves stripped on 75% of available shoots annually) decreased radial growth by approximately 27% at year 2, 37% at year 3, 50% at year 4 and 48% at year 5. We did not observe significant interactions between browsing, temperature and nitrogen availability.4.Synthesis. Our results clearly showed that caribou browsing may limit the growth of B. glandulosa, and thus can potentially limit its expansion. Herbivory should thus be considered when predicting tundra vegetation changes in the Arctic, at least in areas with high herbivore densities.This article is protected by copyright. All rights reserved.
      PubDate: 2017-11-06T04:58:46.550535-05:
      DOI: 10.1111/1365-2745.12899
       
  • Disentangling competitive vs. climatic drivers of tropical forest
           mortality
    • Authors: Michiel Pillet; Emilie Joetzjer, Camille Belmin, Jérôme Chave, Philippe Ciais, Aurélie Dourdain, Margaret Evans, Bruno Hérault, Sebastiaan Luyssaert, Benjamin Poulter
      Abstract: Tropical forest mortality is controlled by both biotic and abiotic processes, but how these processes interact to determine forest structure is not well understood. Using long-term demography data from permanent forest plots at the Paracou Tropical Forest Research Station in French Guiana, we analysed the relative influence of competition and climate on tree mortality. We found that self-thinning is evident at the stand level, and is associated with clumped mortality at smaller scales (
      PubDate: 2017-11-01T04:28:58.422249-05:
      DOI: 10.1111/1365-2745.12876
       
  • Are exotic plants more abundant in the introduced versus native range'
    • Authors: Dean E. Pearson; Özkan Eren, Yvette K. Ortega, Diego Villarreal, Muhyettin Şentürk, M. Florencia Miguel, C. Miguel Weinzettel, Aníbal Prina, José L. Hierro
      Abstract: Many invasion hypotheses postulate that introducing species to novel environments allows some organisms to escape population controls within the native range to attain higher abundance in the introduced range. However, introductions may also allow inherently successful species access to new regions where they may flourish without increasing in abundance.To examine these hypotheses, we randomly surveyed semi-arid grasslands in the native and two introduced ranges (12,000–21,000 km2 per range) to quantify local abundance (mean cover per occupied plot) and occurrence (percentage of 1-m2 plots occupied) for 20 plant introductions that included pest and non-pest species. For each of these metrics, we evaluated relationships between abundance in the introduced vs. native range (1) across all species and (2) according to designated pest status in the introduced range. We predicted that if escape from population controls primarily explained invader success, then these species would be more abundant in the introduced range; while if invader success was driven primarily by intrinsic species attributes, then their abundance would be correlated between ranges.Across all 20 invaders, we found that neither cover nor occurrence metrics were correlated between ranges. While cover was significantly higher in the introduced range, this result was driven by pest species. When the four pest species were excluded, cover but not occurrence was correlated between ranges. Interestingly, whereas cover of pest and non-pest species was comparably low in the native range, pest species cover increased sevenfold in the introduced range.Synthesis. Our results confirm previous findings that local abundance in the native range predicts local abundance in the introduced range for many introduced plants, suggesting that intrinsic species’ attributes may determine most invasion outcomes. However, we also found that some species increased in local abundance in the introduced range, suggesting that changes in biogeographic context may also play an important role. While these latter species were pests, the small sample size precluded strong inferences. Determining what underlies the success of invasive pests remains elusive due to their low representation among introduced species.A biogeographic comparison of 20 plant introductions between the native and introduced ranges demonstrated that non-pest species were similar in abundance between ranges, but pest species increased in abundance in their introduced ranges. These results suggest that some introduced species may achieve pest status due to changes in biogeographic context that facilitate increased abundance in the introduced range.
      PubDate: 2017-11-01T04:28:44.42556-05:0
      DOI: 10.1111/1365-2745.12881
       
  • Canopy-forming macroalgal beds (Sargassum) on coral reefs are resilient to
           physical disturbance
    • Authors: Zoe Loffler; Andrew S. Hoey
      Abstract: Disturbances to ecosystems are often considered in terms of their potential to disrupt the feedbacks maintaining a particular ecosystem regime. The likelihood of doing so, however, will be dependent on the nature of the regime and its resilience to disturbance.Within coral reef ecosystems, shifts from coral- to macroalgal dominance are becoming increasingly common and, once established, are difficult to reverse. Most studies to date have focused on the biological removal of macroalgae by herbivores, however, none have considered the resilience of macroalgal beds to physical removal by storms.We simulated the physical removal of macroalgal biomass from Sargassum beds on an inshore coral reef on Australia's Great Barrier Reef, and monitored recovery for 11 months. Trimming Sargassum biomass but leaving the holdfast intact had no detectable effect on the density, height or biomass of Sargassum compared to adjacent intact, or control, areas after 5 months. In areas where holdfasts were also removed, Sargassum biomass recovered to 50% of control biomass after 11 months.Given the importance of holdfasts to the resilience of Sargassum beds, we also investigated the ability of herbivores to remove and/or damage holdfasts. Exposing pieces of dead coral with attached Sargassum holdfasts to local herbivore assemblages resulted in a 70% decline in the number of holdfasts over 4 months compared to those protected from herbivores.Synthesis. Beds of Sargassum are extremely resilient to the physical removal of algal biomass, and as such, storms alone are unlikely to lead to permanent reductions in Sargassum abundance. Persistent reductions in the abundance of macroalgae on degraded coral reefs will not only require the physical or biological removal of algal biomass, but critically, sufficient densities of herbivores capable of removing holdfasts.Beds of the canopy-forming seaweed, Sargassum, are extremely resilient to the physical removal of algal biomass, and as such, storms alone are unlikely to lead to permanent reductions in Sargassum biomass. Persistent reductions in the abundance of macroalgae on degraded coral reefs will not only require the physical or biological removal of algal biomass, but critically, sufficient densities of herbivores capable of removing holdfasts.
      PubDate: 2017-10-30T19:00:02.233836-05:
      DOI: 10.1111/1365-2745.12875
       
  • Biotic homogenization of regional wetland plant communities within short
           time-scales in the presence of an aggressive invader
    • Authors: Edward P. F. Price; Greg Spyreas, Jeffrey W. Matthews
      Abstract: Biotic homogenization (BH), a process by which β-diversity erodes, represents a severe threat to biodiversity. Wetland plant communities may be especially susceptible to BH; however, this process has rarely been quantified and represents just one of many possible outcomes of compositional change. Likewise, few studies have used more than two timepoints to investigate BH as a dynamic temporal process.To address these issues, we quantified changes in β-diversity amongst 48 herbaceous emergent wetlands across a landscape over four timepoints from 1997 to 2015. Pairwise occurrence- and abundance-based dissimilarity metrics were used to quantify β-diversity. Nonmetric multidimensional scaling was used to map these changes in compositional similarity through time, and repeated measures ANOVA via randomization was used to test for a significant effect of time on β-diversity.Results indicated that herbaceous emergent wetlands homogenized in Illinois over 15 years due to the increased presence and abundance of Phalaris arundinacea and the decline of several other species. Temporal dynamics of β-diversity differed between occurrence- and abundance-based analyses.Synthesis. Using both presence–absence and abundance data to investigate BH helped avoid underestimating the impact of BH on β-diversity, and drew attention to different temporal dynamics in β-diversity at these two resolutions of community structure. This study highlights challenges associated with investigating BH, such as problems documenting the process where homogenization is not occurring in every site in a region, or where sites are converging towards more than one homogenized state. Incorporating concepts like alternative stable states may be helpful in resolving these issues, and present a more realistic picture of ecological change.This study documents biotic homogenization in wetlands throughout the US state of Illinois due to the increased presence and abundance of Phalaris arundinacea and the decline of several other species. This study draws attention to the temporal dynamics of β-diversity that result from homogenization and highlights challenges, such as documenting homogenization when sites converge towards multiple homogenized states.
      PubDate: 2017-10-30T07:12:01.403737-05:
      DOI: 10.1111/1365-2745.12883
       
  • Spatial redistribution of nutrients by large herbivores and dung beetles
           in a savanna ecosystem
    • Authors: Michiel P. Veldhuis; Moniek I. Gommers, Han Olff, Matty P. Berg
      Abstract: Territorial or resting behaviour of large herbivores can cause strong local deposits of dung, in different places than where they graze. Additionally, dung beetles and other macrodetritivores can subsequently affect local nutrient budgets through post-depositional re-dispersion of dung and accompanying nutrients. Such horizontal displacement of nutrients by animals has strong implications for savanna ecosystem functioning, but remains poorly studied as it is notoriously difficult to accurately map these flows and incredibly time-consuming.In an African savanna, with alternating patches of lawn, bunch grasses and trees/shrubs, we undertook such effort and studied nutrient aggregation and redistribution by different large herbivore functional groups and dung beetles for a full growing season. We used movable cages to quantify herbivore consumption rates and measured nutrient return through biweekly dung counts. Furthermore, we estimated the offtake of nitrogen (N) and phosphorus (P) by the dominant megagrazer (white rhinoceros) to middens (dung deposition hotspots). Last, we experimentally measured the removal amount and movement paths of telocoprid dung beetles to quantify their nutrient redistribution effects.Our estimates suggest white rhinoceros to cause a large export of nutrients from grazing areas towards middens resulting in negative nutrient budgets for both lawn and bunch grassland types. Mesograzers (50–600 kg) realized a net nitrogen input towards high forage quality lawn vegetation at the expense of lower quality bunch grasslands. Browsers caused a net flow from trees/shrubs towards grassland patches.Interestingly, while the magnitude of our estimated flows of N consumption and return by large herbivores were rather similar, the P returns were about half of what has been consumed. This is in agreement with ecological stoichiometry theory that predicts that large herbivores should recycle more N than P, due to their relatively high P demand. Furthermore, dung-rolling beetles had a small, but significant, directed movement from lawn to bunch grassland vegetation.Synthesis. We conclude that within-ecosystem nutrient redistributions by animals are important and approximately of the same order of magnitude as regional atmospheric nutrient in and outputs (e.g. fire emissions, atmospheric N deposition, biological N fixation), and hence are important for understanding savanna ecosystem functioning.Animals, especially megagrazers, but also mesograzers/-browsers and even dung beetles are shown to redistribute large amounts of nutrients between different vegetation types. We conclude that within-ecosystem nutrient redistributions by animals are important and approximately of the same order of magnitude as regional atmospheric nutrient in and outputs (e.g. fire emissions, atmospheric N deposition, biological N fixation), and hence are important for understanding savanna ecosystem functioning.
      PubDate: 2017-10-30T07:11:52.91694-05:0
      DOI: 10.1111/1365-2745.12874
       
  • Quantifying antecedent climatic drivers of tree growth in the Southwestern
           US
    • Authors: Drew M. P. Peltier; Jarrett J. Barber, Kiona Ogle
      Abstract: Variation in antecedent (past) climate conditions is likely to govern tree growth over long periods of time. Antecedent conditions are rarely considered in models of tree growth, representing a weakness in quantitative understanding of forest responses to climate variations.We applied the stochastic antecedent modelling (SAM) framework to 367 International Tree Ring Data Bank chronologies in the southwestern US (“Southwest”) representing eight conifer species. To better understand climatic and physiologic controls on tree growth, we quantify the effects of antecedent precipitation, temperature and Palmer Drought Severity Index (PDSI) over 60 months preceding and including the year of ring formation.In Pinus edulis, Pinus ponderosa and Pseudotsuga menziesii, growth responded primarily to recent precipitation and temperature conditions (43%–49% of the response was driven by conditions during the year of ring formation), but to less recent PDSI conditions (>50% of response driven by conditions 13–48 months prior to the year of ring formation), though PDSI significantly affected growth at only 21% of sites. Combining extensive tree-ring data with monthly resolution climate data also reveals key climatic events, such as the effect of monsoon arrival date on growth, especially in P. menziesii, highlighting the ability of the SAM framework to identify climate effects at multiple time-scales.Sensitivity to antecedent climate, baseline growth at average climate conditions and the strength of first order autocorrelation varied spatially, suggesting variation in mean growing conditions, non-structural carbohydrate storage, and/or seasonal precipitation contribution of the North American Monsoon may drive differences in growth sensitivities across species’ ranges.Synthesis. Our findings provide further evidence for multi-year legacy effects of climate conditions, particularly drought metrics, on tree growth. Antecedent climate and especially drought are key drivers of growth in these species, and associated climatic sensitivities and growth indices vary spatially. We argue such factors should be considered in modelling efforts. The spatial variability in antecedent climate sensitivities points to key differences in how different populations within a species range may respond to climate change, particularly if timing of weather events, such as monsoon arrival date, or annual precipitation amounts undergoes significant changes.Application of the Stochastic Antecedent Model to growth data from dendrochronologies in the southwestern US simultaneously reveals the importance of key climatic events like monsoon arrival date, and provides further evidence that trees respond to climate, particularly drought metrics, over long time-scales. Spatially variable responses of different populations to antecedent climate should be considered in predictive modelling efforts of tree growth under projected climate change.
      PubDate: 2017-10-30T07:11:36.408088-05:
      DOI: 10.1111/1365-2745.12878
       
  • Phenology of a dipterocarp forest with seasonal drought: Insights into the
           origin of general flowering
    • Authors: Erin L. Kurten; Sarayudh Bunyavejchewin, Stuart J. Davies
      Abstract: Our understanding of the factors that shape reproductive phenology in Southeast Asian tropical forests comes almost exclusively from studies of everwet, general flowering (GF) forests. Therefore, we examined the phenology of an evergreen dipterocarp forest in a climate exhibiting seasonal drought in Southeast Asia, with the aim of evaluating what evidence it brings to bear on the hypothesis that reproductive phenology in contemporary dipterocarp forests is the product of evolutionarily conserved responses to seasonal drought.We hypothesized that (1) dipterocarp forests that experience seasonal drought would exhibit annual reproduction and seasonality similar to that of forests with similar climates in other parts of the world, (2) within species, flowering frequency would be climate-dependent, not a fixed trait, and (3) climatic events that cue flowering in everwet forests would also cue flowering in seasonally dry forests.From 2001 to 2009, we monitored flowering and fruiting monthly for 1,344 trees (>300 spp.) in a forest in Khao Chong (KC), Thailand that experiences an annual 2–4 month dry season, assessing frequency, duration, seasonality and synchrony of reproduction. We also examined phenological records for trees in three dipterocarp-dominated forests in everwet climates.Reproductive phenology of the KC forest was more similar to tropical forests with similar rainfall seasonality in other parts of the world than it was to dipterocarp-dominated forests in everwet regions of Southeast Asia. The forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season and peak fruiting occurring early in the wet season. Approximately half of all species and individuals reproduced annually, including several species that are known to exhibit “general flowering” in everwet climates. Short dry spells appeared to cue flowering for early flowering species, while later flowering species may have responded to either low precipitation or temperature, consistent with data from everwet forests. GF behaviour also showed significant phylogenetic signal.Synthesis. Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.
      PubDate: 2017-10-25T07:30:45.129413-05:
      DOI: 10.1111/1365-2745.12858
       
  • Soil fungal abundance and plant functional traits drive fertile island
           formation in global drylands
    • Authors: Raúl Ochoa-Hueso; David J. Eldridge, Manuel Delgado-Baquerizo, Santiago Soliveres, Matthew A. Bowker, Nicolas Gross, Yoann Le Bagousse-Pinguet, José L. Quero, Miguel García-Gómez, Enrique Valencia, Tulio Arredondo, Laura Beinticinco, Donaldo Bran, Alex Cea, Daniel Coaguila, Andrew J. Dougill, Carlos I. Espinosa, Juan Gaitán, Reginald T. Guuroh, Elizabeth Guzman, Julio R. Gutiérrez, Rosa M. Hernández, Elisabeth Huber-Sannwald, Thomas Jeffries, Anja Linstädter, Rebecca L. Mau, Jorge Monerris, Aníbal Prina, Eduardo Pucheta, Ilan Stavi, Andrew D. Thomas, Eli Zaady, Brajesh K. Singh, Fernando T. Maestre
      Abstract: Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These “fertile islands” are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale.We conducted a standardized field survey across 236 drylands from five continents. At each site, we measured the composition, diversity and cover of perennial plants. Fertile island effects were estimated at each site by comparing composite soil samples obtained under the canopy of the dominant plants and in open areas devoid of perennial vegetation. For each sample, we measured 15 soil variables (functions) associated with carbon, nitrogen and phosphorus cycling and used the relative interaction index to quantify the magnitude of the fertile island effect for each function. In 80 sites, we also measured fungal and bacterial abundance (quantitative PCR) and diversity (Illumina MiSeq).The most fertile islands, i.e. those where a higher number of functions were simultaneously enhanced, were found at lower elevation sites with greater soil pH values and sand content under semiarid climates, particularly at locations where the presence of tall woody species with a low-specific leaf area increased fungal abundance beneath plant canopies, the main direct biotic controller of the fertile island effect in the drylands studied. Positive effects of fungal abundance were particularly associated with greater nutrient contents and microbial activity (soil extracellular enzymes) under plant canopies.Synthesis. Our results show that the formation of fertile islands in global drylands largely depends on: (1) local climatic, topographic and edaphic characteristics, (2) the structure and traits of local plant communities and (3) soil microbial communities. Our study also has broad implications for the management and restoration of dryland ecosystems worldwide, where woody plants are commonly used as nurse plants to enhance the establishment and survival of beneficiary species. Finally, our results suggest that forecasted increases in aridity may enhance the formation of fertile islands in drylands worldwide.Our results show that the most fertile islands in global drylands are found at lower elevation sites with greater soil pH values and sand content under semiarid climates, particularly at locations where the presence of tall woody species with a low-specific leaf area increased fungal abundance beneath plant canopies. Our study also has broad implications for the management and restoration of dryland ecosystems worldwide, where woody plants are commonly used as nurse plants to enhance the establishment and survival of beneficiary species. Finally, our results suggest that forecasted increases in aridity may enhance the formation of fertile islands in drylands worldwide.
      PubDate: 2017-10-25T07:10:26.904421-05:
      DOI: 10.1111/1365-2745.12871
       
  • Below-ground complementarity effects in a grassland biodiversity
           experiment are related to deep-rooting species
    • Authors: Natalie J. Oram; Janneke M. Ravenek, Kathryn E. Barry, Alexandra Weigelt, Hongmei Chen, Arthur Gessler, Annette Gockele, Hans Kroon, Jan Willem Paauw, Michael Scherer-Lorenzen, Annemiek Smit-Tiekstra, Jasper Ruijven, Liesje Mommer
      Abstract: Below-ground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects.We determined species-specific root standing biomass over depth using molecular techniques (real-time qPCR) in a large grassland biodiversity experiment (one to eight plant species mixtures), in 2 years. Species-specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were linked to the diversity of rooting depths and the averaged rooting depth of the community.Root biomass increased with species richness. This was mainly due to positive interactions (the complementarity effect), which increased with species richness below-ground. In contrast, the selection effect decreased with species richness. Although there was considerable variation in vertical root distribution between species in monocultures, the diversity of rooting strategies did not explain the complementarity effect. Rather, the abundance of deep-rooting species in mixtures (i.e. high community-weighted mean) was significantly related to the complementarity effect. Comparing the “predicted” root distribution (based on monocultures) to the actual distribution in mixtures, we found that mixtures rooted deeper than expected, but this did not better explain the complementarity effect.Synthesis. This study demonstrates that vertical root distributions of species provide only subtle evidence for resource partitioning. We found no evidence that functional diversity in vertical rooting patterns was important for the complementarity effect, in contrast to our expectation that the enhancement of productivity was due to resource partitioning. Alternatively, we found significant but weak relationships between the complementarity effect and deep-rooting communities, based on the community-weighted mean root distribution. This suggests that factors other than below-ground resource partitioning alone may drive the biodiversity–productivity relationship.Below-ground resource partitioning is often hypothesized as the underlying mechanism for the positive relationship between plant species richness and productivity. Here, we tested this hypothesis by measuring species-specific root biomass over depth using molecular techniques in a large grassland biodiversity. Although there was considerable variation in vertical root distribution between species in monocultures, we found no evidence that functional diversity in vertical rooting patterns was important for the complementarity effect. Alternatively, we found significant but weak relationships between the complementarity effect and the mean rooting depth of the plant community. Our study suggests that below-ground resource partitioning alone may not be sufficiently strong to drive the biodiversity–productivity relationship.
      PubDate: 2017-10-25T07:01:40.513289-05:
      DOI: 10.1111/1365-2745.12877
       
  • Winter warming effects on tundra shrub performance are species-specific
           and dependent on spring conditions
    • Authors: Eveline J. Krab; Jonas Roennefarth, Marina Becher, Gesche Blume-Werry, Frida Keuper, Jonatan Klaminder, Juergen Kreyling, Kobayashi Makoto, Ann Milbau, Ellen Dorrepaal
      Abstract: Climate change-driven increases in winter temperatures positively affect conditions for shrub growth in arctic tundra by decreasing plant frost damage and stimulation of nutrient availability. However, the extent to which shrubs may benefit from these conditions may be strongly dependent on the following spring climate. Species-specific differences in phenology and spring frost sensitivity likely affect shrub growth responses to warming. Additionally, effects of changes in winter and spring climate may differ over small spatial scales, as shrub growth may be dependent on natural variation in snow cover, shrub density and cryoturbation.We investigated the effects of winter warming and altered spring climate on growing-season performance of three common and widespread shrub species in cryoturbated non-sorted circle arctic tundra. By insulating sparsely vegetated non-sorted circles and parts of the surrounding heath with additional snow or gardening fleeces, we created two climate change scenarios: snow addition increased soil temperatures in autumn and winter and delayed snowmelt timing without increasing spring temperatures, whereas fleeces increased soil temperature similarly in autumn and winter, but created warmer spring conditions without altering snowmelt timing.Winter warming affected shrub performance, but the direction and magnitude were species-specific and dependent on spring conditions. Spring warming advanced, and later snowmelt delayed canopy green-up. The fleece treatment did not affect shoot growth and biomass in any shrub species despite decreasing leaf frost damage in Empetrum nigrum. Snow addition decreased frost damage and stimulated growth of Vaccinium vitis-idaea by c. 50%, while decreasing Betula nana growth (p 
      PubDate: 2017-10-23T04:28:03.38528-05:0
      DOI: 10.1111/1365-2745.12872
       
  • Niche differentiation and expansion of plant species are associated with
           mycorrhizal symbiosis
    • Authors: Maret Gerz; C. Guillermo Bueno, Wim A. Ozinga, Martin Zobel, Mari Moora
      Abstract: Mycorrhizal symbiosis is a widespread association between plant roots and mycorrhizal fungi, which is thought to contribute to plant niche differentiation and expansion. However, this has so far not been explicitly tested.To address the effect of mycorrhizal symbiosis on plants’ realized niches, we addressed how mycorrhizal status (i.e. the frequency of occurrence of mycorrhizal symbiosis), flexibility (i.e. the ability to grow both with and without mycorrhizal symbiosis) and type of a plant species affect the realized niche optima, widths and volumes. For this, we used co-occurrence data from the flora of the Netherlands along soil fertility, moisture, pH, salinity, light and temperature gradients. Phylogenetic dependency of the species was taken into account using phylogenetic generalized least squares models.We show that facultatively and flexibly mycorrhizal plants have the widest niches compared to non-mycorrhizal and obligately mycorrhizal, and inflexible plants respectively. Among obligate plant symbionts, ecto- and ericoid mycorrhizal plants exhibited the widest niches compared to plants with other mycorrhizal types. Also, plants with different mycorrhizal statuses and types differed in their realized niche optima.Synthesis. Our results indicate that mycorrhizal symbiosis mediates plant niche differentiation and expansion, facilitating the understanding of current distribution patterns of plant species, as well as predicting shifts in plant distribution and dominance due to environmental changes.Our results indicate that mycorrhizal symbiosis mediates plant niche differentiation and expansion, facilitating the understanding of current distribution patterns of plant species, as well as predicting shifts in plant distribution and dominance due to environmental changes.
      PubDate: 2017-10-23T04:25:25.923264-05:
      DOI: 10.1111/1365-2745.12873
       
  • Intracontinental plant invader shows matching genetic and chemical
           
    • Authors: Lisa Johanna Tewes; Florian Michling, Marcus A. Koch, Caroline Müller
      Abstract: Whereas many studies have revealed mechanisms driving plant invasions between continents, research on intracontinental range expanders is scarce. Therefore, we studied genetic, chemical and ecological traits of a range-expanding Brassicaceae, assuming that high genetic diversity should maintain chemical variation, which potentially benefits the invasion success. Moreover, we expected that within-individual defence diversity plays an essential role in biotic interactions.We compared Bunias orientalis L. plants from 16 populations of native, invasive or exotic non-invasive origin. The genetic structure was investigated by analysing the plastid DNA and amplified fragment length polymorphisms. For characterisation of the leaf chemistry, metabolic fingerprinting and profiling of glucosinolates as defence compounds were performed. The plant defence potential was tested using the generalist herbivore Mamestra brassicae.We found two major genetic lineages, which were mirrored in distinct chemical fingerprints of the plants. Genetic differentiation patterns point to a multiple introduction history of B. orientalis underlying the range expansion. Moreover, the genetic distance between individuals was correlated with the distance in chemical features. Genetic diversity tended to be reduced in potential leading edge (exotic) populations and was positively associated with quantitative metabolic diversity. Concentrations of indole glucosinolates were elevated in non-native populations, and high glucosinolate diversity was associated with low herbivore survival.Synthesis. This study suggests that the invasion success of this species may be facilitated by high chemical variation within populations. Moreover, high defence diversity within individuals of a population might be the main factor reducing herbivory and can be more important than the total concentration of defences. The combination of genetic and chemical analyses combined with bioassays revealed to be a powerful tool to study the differentiation between native and non-native populations and should be applied more often to explore intraspecific divergence.This study suggests that the invasion success of this species may be facilitated by high chemical variation within populations. Moreover, high defence diversity within individuals of a population might be the main factor reducing herbivory and can be more important than the total concentration of defences. The combination of genetic and chemical analyses combined with bioassays revealed to be a powerful tool to study the differentiation between native and non-native populations and should be applied more often to explore intraspecific divergence.
      PubDate: 2017-10-12T03:25:35.082466-05:
      DOI: 10.1111/1365-2745.12869
       
  • A global analysis of elevational gradients in leaf herbivory and its
           underlying drivers: Effects of plant growth form, leaf habit and climatic
           correlates
    • Authors: Andrea Galmán; Luis Abdala-Roberts, Shuang Zhang, Jorge C. Berny-Mier y Teran, Sergio Rasmann, Xoaquín Moreira
      Abstract: Research on elevational gradients in species interactions holds that herbivore pressure increases towards warmer and more stable climates found at lower elevations. However, the generality of this expectation has been challenged by recent studies reporting no evidence of expected trends or even positive associations between elevation and herbivory, presumably due to uncontrolled biotic and abiotic factors influencing such relationships.Using a world-wide dataset of insect leaf herbivory including 1,027 plant species and spanning an elevation gradient of 2,755 m, we tested if elevational gradients in herbivory were contingent on whether species were found at tropical vs. temperate latitudes, plant growth form (non-woody vs. woody species), and leaf habit (deciduous vs. evergreen woody species). In addition, we tested the influence of climatic correlates of elevation presumably underlying such elevational gradients.Although there was no evidence of an overall relationship between elevation and damage, we found that elevational gradients in herbivory were contingent on species growth form whereby herbivory increased towards lower elevations for woody species, but no gradient was observed for non-woody species. We further found that elevational gradients in herbivory were contingent on leaf habit as herbivory increased towards lower elevations for deciduous species, but no gradient was present for evergreen species. Elevational variation in damage was not contingent upon latitudinal region. Finally, analyses of climatic factors indicated that although a significant association between temperature and herbivory for woody species was detected, the elevational gradient in leaf herbivory remained largely unchanged after accounting for temperature and precipitation, suggesting that climate does not fully account for the gradient.Synthesis. This study delivers the first global assessment of elevational gradients in leaf herbivory and emphasizes the role of plant (e.g. life-history or defensive) traits and climatic factors in shaping elevational gradients in herbivory.This study provides a global assessment of elevational gradients in leaf herbivory across tropical and temperate regions, and further explores the mechanistic underpinnings of such gradients by evaluating the influence of plant life-history traits (e.g. growth form and leaf habit) and climatic factors
      PubDate: 2017-10-11T04:05:26.497352-05:
      DOI: 10.1111/1365-2745.12866
       
  • Long-term population dynamics: Theory and reality in a peatland ecosystem
    • Authors: Simon E. Connor; Daniele Colombaroli, Federico Confortini, Erika Gobet, Boris P. Ilyashuk, Elena A. Ilyashuk, Jacqueline F.N. Leeuwen, Mariusz Lamentowicz, Willem O. Knaap, Elena Malysheva, Aldo Marchetto, Nino Margalitadze, Yuri Mazei, Edward A.D. Mitchell, Richard J. Payne, Brigitta Ammann
      Abstract: Population dynamics is a field rich in theory and poor in long-term observational data. Finding sources of long-term data is critical as ecosystems around the globe continue to change in ways that current theories and models have failed to predict. Here we show how long-term ecological data can improve our understanding about palaeo-population change in response to external environmental factors, antecedent conditions and community diversity.We examined a radiometrically dated sediment core from the Didachara Mire in the mountains of south-western Georgia (Caucasus) and analysed multiple biological proxies (pollen, fern spores, non-pollen palynomorphs, charcoal, diatoms, chrysophyte cysts, midges, mites and testate amoebae). Numerical techniques, including multivariate ordination, rarefaction, independent splitting and trait analysis, were used to assess the major drivers of changes in community diversity and population stability. Integrated multi-proxy analyses are very rare in the Caucasus, making this a unique record of long-term ecological change in a global biodiversity hotspot.Synthesis. Population changes in the terrestrial community coincided primarily with external environmental changes, while populations within the peatland community were affected by both internal and external drivers at different times. In general, our observations accord with theoretical predictions that population increases lead to greater stability and declines lead to instability. Random variation and interspecific competition explain population dynamics that diverged from predictions. Population change and diversity trends were positively correlated in all taxonomic groups, suggesting that population-level instability is greater in more diverse communities, even though diverse communities are themselves more stable. There is a continuing need to confront population theory with long-term data to test the predictive success of theoretical frameworks, thereby improving their ability to predict future change.Palaeo-data from a peatland ecosystem support the key predictions of population dynamics theory—that population increases tend to lead to greater stability and declines lead to instability. Random variation and interspecific competition explain population dynamics that diverged from predictions. Population change and diversity trends were positively correlated in all taxonomic groups.
      PubDate: 2017-10-11T03:21:21.715289-05:
      DOI: 10.1111/1365-2745.12865
       
  • Beyond biomass: Soil feedbacks are transient over plant life stages and
           alter fitness
    • Authors: Jan-Hendrik Dudenhöffer; Anne Ebeling, Alexandra-Maria Klein, Cameron Wagg
      Abstract: Plants influence associated soil biotic communities that in turn can alter the performance of the subsequently growing plants. Although such “plant–soil feedbacks” (PSFs) are considered as important drivers of plant community assembly, past PSF studies have mainly addressed plant biomass production. However, plant performance is not only the production of biomass but comprises a sequence of different life stages: from seed germination over vegetative growth up to the production of a viable progeny.Here, we assessed the effects of soil biotic communities that were previously conditioned for 3 years by a focal plant species monoculture or species mixtures on key plant life stages from germination and vegetative growth to flowering and the production of viable seeds. We used three common grassland herb species that were grown in a sterile substrate and inoculated with a sterile control soil or with living soils. Living soils were conditioned either by the focal species in monoculture or a four- or eight-species mixture that included the focal species to represent a decrease in the target plants’ conspecific influence on the soil communities.We show that the effect of soil biota changed from positive at the plants’ juvenile life stages to neutral or negative at the plants’ adult life stages and ultimately decreased plant fitness. A higher conspecific influence on the soil communities pronounced the positive effects at the juvenile life stage but also the negative effects at adult life stages. Further, we observed direct soil biotic effects on flower production and plant fitness that were not mediated by adult biomass production. This suggests that soil biotic effects may alter plant resource allocation and even may have transgenerational effects on plant fitness.Synthesis. We conclude that there is no overarching effect of soil biota that remains consistent at all the life stages of a plant. Thus, our results highlight the importance to consider plant life stage and ultimately plant fitness especially when plant–soil interactions are used to explain plant community dynamics.Following soil biotic effects and feedbacks along the life cycles of three plant species, our study suggests that plant responses to soil biota are transient across plant life stages. Effects observed during the vegetative life stage not necessarily reflect successful plant reproduction. The temporal variability of soil biotic effects highlights the importance to consider plant responses beyond biomass production, especially when plant–soil biotic interactions are used to explain plant species coexistence and community dynamics.
      PubDate: 2017-10-11T03:20:51.786003-05:
      DOI: 10.1111/1365-2745.12870
       
  • The influence of residence time and geographic extent on the strength of
           plant–soil feedbacks for naturalised Trifolium
    • Authors: Kevin J. McGinn; Wim H. Putten, Philip E. Hulme, Natasha Shelby, Carolin Weser, Richard P. Duncan
      Abstract: Release from natural enemies is considered an important mechanism underlying the success of plants introduced to new regions, but the degree to which alien plant species benefit from enemy release appears highly variable and context-dependent. Such variation could arise if enemy release is a transient phenomenon, whereby alien plant species initially escape but subsequently accumulate enemies in their new regions.To evaluate this hypothesis in terms of soil biota, we used 11 Trifolium (clover) species introduced to New Zealand from Europe to test whether species resident for longer or with a larger geographic extent in New Zealand were more adversely affected by soil communities in the introduced range, as expected if species have accumulated inhibitory soil biota over time. We used plant–soil feedback (PSF) experiments to compare the effect of soil biota on the growth of the Trifolium species in soil from their introduced (New Zealand) and native (Spain and the United Kingdom) ranges. We applied a novel statistical approach aimed at isolating the impact of antagonistic soil biota by accounting for variation in plant growth due to mutualistic rhizobia bacteria.The between-range differences in PSF varied considerably among the Trifolium species: some species were released from inhibitory PSF in the introduced range, but the majority experienced similar PSF in both ranges. Averaged over all 11 Trifolium species, PSF was less inhibitory in the introduced than in the native range, implying some release from soil-borne enemies. However, neither residence time nor geographic extent in the introduced range was significantly correlated with the strength of release from inhibitory PSF.Synthesis. Our multispecies study provides some evidence that alien plants can escape antagonistic soil biota in their introduced range, but highlights how plant–soil feedback responses can be highly variable among congeneric plant species in the same region. Our results do not support the hypothesis that the release from inhibitory plant–soil feedback is transient, questioning the generality of this phenomenon.Release from inhibitory plant–soil feedback for 11 Trifolium species introduced to New Zealand is not related to residence time nor geographic extent.
      PubDate: 2017-10-11T03:20:23.456225-05:
      DOI: 10.1111/1365-2745.12864
       
  • Specific leaf area predicts dryland litter decomposition via two
           mechanisms
    • Authors: Guofang Liu; Lei Wang, Li Jiang, Xu Pan, Zhenying Huang, Ming Dong, Johannes H. C. Cornelissen
      Abstract: Litter decomposition plays important roles in carbon and nutrient cycling. In dryland, both microbial decomposition and abiotic degradation (by UV light or other forces) drive variation in decomposition rates, but whether and how litter traits and position determine the balance between these processes is poorly understood.We investigated relationships between litter quality and their decomposition rates among diverse plant species in a desert ecosystem in vertically contrasting positions representing distinct decomposition environments driven by different relative contributions of abiotic and microbial degradation. Thereto, leaf litter samples from 17 desert species were sealed into litterbags and placed on the soil surface under strong solar exposure vs. shade conditions, or buried in the soil at 10 cm depth, for a whole year.Litter decomposition rates were 21% and 17% higher in burial and light-exposed treatments, respectively, than those in shade. Leaf traits, i.e. specific leaf area (SLA), litter C:N ratio and lignin concentration could predict litter decomposition to some degree, but their predictive power was dependent on litter position. However, multiple linear regressions showed that SLA, litter C and P significantly affected k values for leaf litter decomposition besides litter position, with SLA standing out as a strong determinant of litter decomposition rate as related either to solar radiation or the environment below the soil surface. Furthermore, the interspecific differences in litter decomposition rates decreased over time, implying that afterlife effects of leaf traits on decomposition were attenuated.Synthesis. These findings suggest that abiotic photodegradation and soil burial mediated microbial decomposition could be responsible for higher than expected litter turnover in dryland. They point to a dual role of specific leaf area (SLA) as a promotor of decomposition rates: via relative exposure of the leaf surface to abiotic factors such as UV light vs. to soil moisture and microbes under soil burial.These findings suggest that abiotic photodegradation and soil burial–mediated microbial decomposition could be responsible for higher than expected litter turnover in dryland. They point to a dual role of specific leaf area as a promotor of decomposition rates: via relative exposure of the leaf surface to abiotic factors such as UV light vs. to soil moisture and microbes under soil burial.
      PubDate: 2017-10-09T05:10:36.63378-05:0
      DOI: 10.1111/1365-2745.12868
       
  • Effects of arbuscular mycorrhizal fungi on above-ground tri-trophic
           interactions are contingent upon plant genetic effects of cross type in
           the perennial herb Ruellia nudiflora
    • Authors: Blanca Mejia-Alva; José Ramos-Zapata, Luis Abdala-Roberts, Víctor Parra-Tabla
      Abstract: Recent work has improved our understanding of the linkages between above- and below-ground interactions mediated by plants. However, relatively few of the studies conducted thus far have focused on multi-trophic interactions (i.e. beyond two trophic levels) and the influence of plant genetic intraspecific variation on these dynamics has rarely been addressed.We tested the effect of arbuscular mycorrhizal fungi (AMF) on above-ground tri-trophic interactions associated with the canopy of the perennial herb Ruellia nudiflora, and further determined whether genetic effects due to cross type (i.e. whether a plant originated from self- or cross-pollination) influenced these interactions.We propagated plants originating from self- or cross-pollination, and within each category inoculated half of the plants with AMF. We subsequently established a common garden where plants were exposed to naturally occurring seed-eating caterpillars and their parasitoids. We measured plant growth, fruit output, calculated the proportion of attacked fruits by the caterpillar and the proportion of parasitized caterpillars, and also estimated the proportion of “rescued” seeds by parasitoids representing an indirect positive effect of the third trophic level on the plant by reducing caterpillar consumption.Arbuscular mycorrhizal fungi drove 18% and 15% increases in plant growth and fruit output respectively, and drove a 25% reduction in caterpillar fruit attack, but did not influence parasitism or parasitoid seed “rescue.” In contrast, cross type did not influence growth, fruit number, herbivore attack, parasitism or seed rescue. More importantly, however, we found a significant AMF by cross type interaction on caterpillar attack, where AMF significantly reduced fruit attack (by 30%) in progeny from cross-pollination but did not influence herbivory in progeny from self-pollination.Synthesis. Results indicate that effects of arbuscular mycorrhizal fungi on above-ground interactions are contingent upon plant intraspecific variation originating from cross type, which is likely a common source of variation in associated interactions for plants with mixed mating systems. Further studies examining plant-mediated below- and above-ground interactions should consider the influence of specific sources of plant genetic variation, as well as address the consequences of such dynamics for interactions beyond two trophic levels.We investigate the effects of arbuscular mycorrhizal fungi (AMF) on above-ground tri-trophic interactions associated with the perennial herb Ruellia nudiflora, and further test the contingency of such effects upon plant cross type. We show that AMF effects on above-ground interactions are contingent upon plant intraspecific variation originating from cross type, which is likely a common source of variation in associated interactions for plants with mixed mating systems.
      PubDate: 2017-10-02T05:01:34.459912-05:
      DOI: 10.1111/1365-2745.12859
       
  • Herbivore community determines the magnitude and mechanism of nutrient
           effects on subtropical and tropical seagrasses
    • Authors: Justin E. Campbell; Andrew H. Altieri, Lane N. Johnston, Caitlin D. Kuempel, Richard Paperno, Valerie J. Paul, J. Emmett Duffy
      Abstract: Numerous studies have examined the combined effects of nutrients (bottom-up control) and consumers (top-down control) on ecosystem structure and functioning. While it is recognized that both can have important effects, there remains a limited understanding of how their relative importance shifts across large spatial scales where consumer functional types can vary.Using seagrasses as a model ecosystem, we explore the effects of ambient variation in herbivore functional composition on the relative importance of bottom-up and top-down forcings. Distributed experiments were conducted across four Western Atlantic sites that encompassed a gradient in consumer composition. Herbivores at two subtropical sites were predominantly comprised of small crustacean invertebrates (mesograzers that consume epiphytic algae), while herbivores at two tropical sites were dominated by large macrograzers (sea urchins and herbivorous fishes that directly consume seagrass biomass).To test the relative importance of bottom-up and top-down factors at each site, we manipulated nutrient supply, mesograzer abundance, and the presence of macrograzers (mainly herbivorous fishes) in a fully factorial design over a 14-week growing season. Seagrass above-ground biomass, shoot density, canopy cover, leaf productivity and epiphyte mass were measured as indicators of habitat structure and productivity.Overall, nutrient addition elicited a strong response across sites, causing widespread loss of seagrass biomass and shoot density. However, the mechanisms driving these declines strongly varied as a function of resident herbivore identity. Seagrass loss at tropical sites was attributable to macrograzers, which increased their direct consumption of fertilized, nutrient-rich seagrass. Conversely, at the subtropical sites, nutrient loading caused seagrass declines associated with the proliferation of epiphytic algae, but only in locations where mesograzer abundance was low.Synthesis. Our results confirm that nutrient enrichment generally has negative effects on seagrasses, but that the underlying mechanisms vary and may depend upon herbivore presence and functional identity. Along a subtropical to tropical gradient, the adverse effects of nutrient loading may switch from competitive algal overgrowth to a stimulation of seagrass consumption. Thus, in the tropics, top-down and bottom-up factors can act in combination, and in the same direction, to contribute to habitat loss.Our results confirm that nutrient enrichment has negative effects on seagrasses, but the mechanisms vary and depend upon herbivore presence and identity. Along a subtropical to tropical gradient, the adverse effects of nutrient loading may switch from competitive algal overgrowth to a stimulation of seagrass consumption, as in this photo where nutrients stimulated herbivory by macrograzers that cleared seagrass from an experimental plot. Thus, in the tropics, top-down and bottom-up factors can act in combination, and in the same direction, to contribute to habitat loss.
      PubDate: 2017-10-02T05:01:30.930333-05:
      DOI: 10.1111/1365-2745.12862
       
  • Linking resource availability and heterogeneity to understorey species
           diversity through succession in boreal forest of Canada
    • Authors: Praveen Kumar; Han Y. H. Chen, Sean C. Thomas, Chander Shahi
      Abstract: Understorey vegetation comprises the majority of species diversity and contributes greatly to ecosystem functioning in boreal forests. Although patterns of understorey abundance, species diversity and composition associated with forest stand development are well researched, mechanisms driving these patterns remain largely speculative.We sampled fire-origin stands of varying stand ages and overstorey compositions on mesic sites of the boreal forest of Canada and used structural equation modelling (SEM) to link time since fire (stand age), light availability and heterogeneity, substrate heterogeneity and soil nitrogen to understorey vegetation cover and species diversity.The most parsimonious model for total understorey cover showed a positive direct effect of stand age (r = .43) and an indirect effect via mean light level (0.18) and shrub cover (−0.11), with a positive total effect (0.50); the per cent broadleaf canopy had a direct negative effect (−0.22) and an indirect effect via shrub cover (−0.11). The model for total understorey species richness showed an indirect effect of stand age via mean light (0.24), light heterogeneity (0.10) and substrate heterogeneity (0.07), with a positive total effect (0.52); per cent broadleaf canopy had an indirect effect via light heterogeneity (0.09), and substrate heterogeneity (−0.10). Soil nitrogen did not significantly influence either understorey cover or species richness. The models for vascular plants followed similar trends to those for total understorey cover and species richness; however, there was an opposite indirect effect of light heterogeneity for both cover and species richness of non-vascular plants. Shrub cover had positive direct and negative direct and indirect effects on both vascular and non-vascular cover and species richness.Synthesis. Our findings indicate that understorey cover and species diversity are driven by time since disturbance, light availability as influenced by overstorey and shrub layers, but with important additional effects mediated by light and substrate heterogeneity. Non-vascular understorey vegetation is more strongly determined by time since disturbance than vascular vegetation, and negatively affected by broadleaf tree abundance. The overall results highlight the importance of colonization, light availability and heterogeneity, substrate specialization and growth dynamics in determining successional patterns of boreal forest understorey vegetation.Although patterns of understorey abundance, species diversity and composition associated with forest stand development are well researched, mechanisms driving these patterns remain largely speculative. Our findings highlight the conclusion that multiple mechanisms, including time since colonization, light availability and heterogeneity, and substrate heterogeneity determine patterns of understorey vegetation abundance and diversity through forest stand development following replacing disturbances.
      PubDate: 2017-10-02T05:01:09.92087-05:0
      DOI: 10.1111/1365-2745.12861
       
  • Contrasting habitat and landscape effects on the fitness of a long-lived
           grassland plant under forest encroachment: Do they provide evidence for
           extinction debt'
    • Authors: Guillem Bagaria; Ferran Rodà, Maria Clotet, Silvia Míguez, Joan Pino
      Abstract: Habitat loss, fragmentation and transformation threaten the persistence of many species world-wide. Population and individual fitness are often compromised in small, degraded and isolated habitats, but extinction can be a slow process and extinction debts are common.Long-lived species are prone to persist as remnant populations in low-quality habitats for a long time, but the population- and individual-level mechanisms of extinction debt remain poorly explored so far.We here investigate the mechanisms involved in the long-term persistence of the common grassland specialist, long-lived, clonal plant Aphyllanthes monspeliensis L. (Asparagaceae) after forest encroachment into semi-natural Mediterranean calcareous grasslands in Catalonia (NE Iberian Peninsula). For this purpose, we assess vegetative (above-ground and below-ground) and reproductive plant performance indicators and their habitat and landscape (current and historical) drivers.We confirm the existence of an extinction debt for this species, since current plant frequency is related to historical but not current connectivity, and we also find a positive effect of historical connectivity on seed set. In addition, current tree cover negatively affects individual size and above-ground/below-ground biomass ratio, and biotic soil acidification leads to a reduction in the flowering probability of individuals and stems.However, we also find that current connectivity negatively affects flowering and that tree cover enhances seed set. The forestation process, thus, also exerts a positive effect on some fitness traits, probably by providing a moister environment.Synthesis. Habitat loss and deterioration result in a decreased vegetative performance of Aphyllanthes monspeliensis, a grassland specialist, but show contrasting effects on its reproductive performance. This suggests that the species would perform better in open forests than grasslands in a context of climate change. However, further forest encroachment would increase light competition and soil acidification, threatening its persistence and promoting the payment of the extinction debt if no conservation measures are taken, like opening gaps in forests and enhancing grassland connectivity.Habitat loss and deterioration result in a decreased vegetative performance of Aphyllanthes monspeliensis, a grassland specialist, but show contrasting effects on its reproductive performance. This suggests the species would perform better in open forests than grasslands in a context of climate change, although further forest encroachment would promote the payment of the extinction debt if no conservation measures are taken.
      PubDate: 2017-10-02T05:00:49.717732-05:
      DOI: 10.1111/1365-2745.12860
       
  • Climate warming as a driver of tundra shrubline advance
    • Authors: Isla H. Myers-Smith; David S. Hik
      Abstract: Climate warming is predicted to alter ecological boundaries in high-latitude ecosystems including the elevational or latitudinal extent of tall shrubs in Arctic and alpine tundra. Over 60 studies from 128 locations around the tundra biome have investigated shrub expansion in tundra ecosystems; however, only six studies test whether shrublines are actually advancing up hill-slopes or northward into tundra where tall shrubs are currently absent.We test the hypothesis that willow shrublines have expanded to higher elevations in relation to climate across a 50 × 50 km area in the Kluane Region of the southwest Yukon Territory, Canada by surveying of 379 shrubs at 14 sites and sampling of 297 of the surveyed shrubs at 10 sites. We compared growth and recruitment to climate variables to test the climate sensitivity of shrub increase using annual radial growth analysis, age distributions and repeat field surveys to estimate the current rate of shrubline advance.We found consistent and increasing rates of recruitment of alpine willows, with estimates of faster advancing shrublines on shallower hill-slopes. Mortality was extremely low across the elevation gradient. Aspect, elevation and species identity did not explain variation in recruitment patterns, suggesting a regional factor, such as climate, as the driver of the observed shrubline advance.Annual radial growth of willows was best explained by variation in summer temperatures, and recruitment pulses by winter temperatures. Measured recruitment rates are ~20 ± 5 individuals per hectare per decade (M ± SE) and measured rates of increased shrub cover of ~5 ± 1% per decade (M ± SE) measured at the Pika Camp site between field surveys in 2009 and 2013. Our results suggest that shrubline will continue to advance over the next 50 years, if growing conditions remain suitable. However, if future conditions differ between summer and winter seasons, this could lead to contrasting trajectories for recruitment vs. growth, and influence the vegetation change observed on the landscape.Synthesis. Our findings in the context of a review of the existing literature indicate that elevational and latitudinal shrublines, like treelines, are advancing in response to climate warming; however, the trajectories of change will depend on the climate drivers controlling recruitment vs. growth.Climate warming is predicted to alter ecological boundaries in high-latitude ecosystems including the elevational or latitudinal extent of tall shrubs in Arctic and alpine tundra. Our findings indicate that elevational and latitudinal shrublines, like treelines, are advancing in response to climate warming; however, the trajectories of change will depend on the climate drivers controlling recruitment versus growth.
      PubDate: 2017-09-25T09:41:20.376944-05:
      DOI: 10.1111/1365-2745.12817
       
  • Environmental controls on the causes and functional consequences of tree
           species diversity
    • Authors: Akira S. Mori
      Abstract: Knowledge of the functional consequences of biodiversity is increasing through studies of both experimental systems and natural systems. Community assembly theory has also helped to reveal the causes of biodiversity organization. However, the causes and consequences of biodiversity have been discussed in parallel and simultaneous consideration of both has been limited, even though they are both influenced by regional environmental conditions.To understand the relationship between biodiversity and productivity, I focused on the linkages between the number of tree species and biomass productivity across forest biomes under a range of bioclimatic conditions.I found that high tree diversity generally increased productivity. This was primarily due to a selection process that results from a high probability of having high-performance species and their dominance at high diversity, regardless of the biome. In less-productive biomes, the residual importance of diversity, which likely reflects other forms of biological interactions (including species complementarity), increased productivity.These findings of differential diversity effects under different environmental conditions are consistent with the existing theory of community assembly, which predicts a shift in the assembly process from stochasticity to determinism with increasing environmental harshness. Analyses based on functional trait diversity also supported this theory: stochastic assembly (resulting in the selection effect) and deterministic assembly (possibly resulting from interspecific niche differences) became more important in productive and less-productive biomes, respectively.Synthesis. Increasing our understanding of the causalities between diversity and other characteristics, such as productivity, is crucial, particularly for forest ecosystems, because of the increasing interest in productivity-related ecosystem services supported by diverse assemblages of trees.This study found differential diversity effects under different environmental conditions, which are consistent with the existing theory of community assembly. Increasing our understanding of the causalities between diversity and other characteristics, such as productivity, is crucial, particularly for forest ecosystems, because of the increasing interest in productivity-related ecosystem services supported by diverse assemblages of trees.
      PubDate: 2017-09-25T09:40:51.803786-05:
      DOI: 10.1111/1365-2745.12851
       
  • Above-ground biomass is driven by mass-ratio effects and stand structural
           attributes in a temperate deciduous forest
    • Authors: Alexander T. Fotis; Stephen J. Murphy, Raleigh D. Ricart, Meghna Krishnadas, James Whitacre, John W. Wenzel, Simon A. Queenborough, Liza S. Comita
      Abstract: Forest ecosystems are critical for the global regulation of carbon (C), a substantial portion of which is stored in above-ground biomass (AGB). While it is well understood that taxonomic and functional composition, stand structure and environmental gradients influence spatial variation in AGB, the relative strengths of these drivers at landscape scales have not been investigated in temperate forests. Furthermore, when biodiversity enhances C storage, it is unclear whether it is through mass-ratio effects (i.e. the dominant trait in communities regulates AGB) or through niche complementarity (i.e. increased AGB due to interspecific resource partitioning).To address these mechanisms, we analysed data from a census of 28,262 adult trees sampled across 900 ha of temperate deciduous forest in southwestern Pennsylvania. We used data on four key plant functional traits to determine if (1) there is a positive relationship between species diversity and AGB and (2) whether this is due to mass-ratio effects or niche complementarity. We also sought to (3) identify the physical stand structural attributes and topographic variables that influence AGB across this landscape.We found AGB was positively related to species richness and negatively related to species evenness, albeit weakly, while functional diversity indices had neutral effects. Above-ground biomass was enhanced in communities dominated by traits related to greater maximum tree height, deeper minimum rooting depths and larger seeds. Most importantly, areas with high AGB were dominated by Acer saccharum and Liriodendron tulipifera. Overall, these results support mass-ratio effects, with little evidence for niche complementarity.Synthesis. Stand structure, topography, and species and functional composition, but not taxonomic or functional diversity, were found to be key drivers of above-ground biomass at landscape scales (
      PubDate: 2017-09-21T05:20:59.814877-05:
      DOI: 10.1111/1365-2745.12847
       
  • Early- and late-flowering guilds respond differently to landscape spatial
           structure
    • Authors: Jesse E. D. Miller; Anthony R. Ives, Susan P. Harrison, Ellen I. Damschen
      Abstract: Species with unique phenologies have distinct trait syndromes and environmental affinities, yet there has been little exploration of whether community assembly processes differ for plants with different phenologies. In this study, we ask whether early- and late-blooming species differ in the ways that dispersal, persistence and resource acquisition traits shape plant occurrence patterns in patchy habitats.We sampled plant communities in 51 Ozark dolomite glade grasslands, which range in size from 100 ha. We modelled the occurrence of 71 spring- and 43 summer-blooming grassland species in these patches, using as predictors both environmental variables (landscape structure, soil resources) and plant traits related to dispersal, longevity and resource acquisition. We were especially interested in how the environmental variables and plant traits interacted to determine the occurrence of phenological strategies in habitats that vary in size and isolation.Summer-blooming species with better persistence and dispersal abilities had higher relative frequencies in smaller, more isolated habitat patches, and summer-blooming species with higher specific leaf area—suggesting fast growth and low stress tolerance—were more likely to occur in patches with greater soil organic matter and clay content. However, spring-blooming species showed much weaker interactions between functional traits and environmental gradients, perhaps because environmental conditions are less harsh in spring than in summer.Synthesis. Several axes of plant life-history variation may simultaneously influence community responses to habitat connectivity. In this case, explicitly considering plant phenology helped identify generalizable relationships between functional traits and landscape spatial structure.Several axes of plant life-history variation may simultaneously influence community responses to habitat connectivity. In this case, explicitly considering plant phenology helped identify generalizable relationships between functional traits and landscape spatial structure.
      PubDate: 2017-09-18T06:16:48.925434-05:
      DOI: 10.1111/1365-2745.12849
       
  • Growth strategies and threshold responses to water deficit modulate
           effects of warming on tree seedlings from forest to alpine
    • Authors: Brynne E. Lazarus; Cristina Castanha, Matthew J. Germino, Lara M. Kueppers, Andrew B. Moyes
      Abstract: Predictions of upslope range shifts for tree species with warming are based on assumptions of moisture stress at lower elevation limits and low-temperature stress at high-elevation limits. However, recent studies have shown that warming can reduce tree seedling establishment across the entire gradient from subalpine forest to alpine via moisture limitation. Warming effects also vary with species, potentially resulting in community shifts in high-elevation forests.We examined the growth and physiology underlying effects of warming on seedling demographic patterns. We evaluated dry mass (DM), root length, allocation above- and below-ground, and relative growth rate (RGR) of whole seedlings, and their ability to avoid or endure water stress via water-use efficiency and resisting turgor loss, for Pinus flexilis, Picea engelmannii and Pinus contorta seeded below, at and above tree line in experimentally warmed, watered and control plots in the Rocky Mountains, USA. We expected that growth and allocation responses to warming would relate to moisture status and that variation in drought tolerance traits would explain species differences in survival rates.Across treatments and elevations, seedlings of all species had weak turgor-loss resistance, and growth was marginal with negative RGR in the first growth phase (−0.01 to −0.04 g g−1 day−1). Growth was correlated with soil moisture, particularly in the relatively small-seeded P. contorta and P. engelmannii. Pinus flexilis, known to have the highest survivorship, attained the greatest DM and longest root but was also the slowest growing and most water-use efficient. This was likely due to its greater reliance on seed reserves. Seedlings developed 15% less total DM, 25% less root DM and 11% shorter roots in heated compared with unheated plots. Higher temperatures slightly increased DM, root length and RGR where soils were wettest, but more strongly decreased these variables under drier conditions.Synthesis. The surprising heat inhibition of tree seedling establishment at the cold edge of forests appears to have a physiological basis: newly germinated seedlings have poor moisture stress tolerance, which appears related to marginal initial growth and heavy reliance on seed reserves. Variation in these attributes among tree species at tree line helps explain their different climate responses.The surprising heat inhibition of tree seedling establishment at the cold edge of forests appears to have a physiological basis: newly germinated seedlings have poor moisture stress tolerance, which appears related to marginal initial growth and heavy reliance on seed reserves. Variation in these attributes among tree species at tree line helps explain their different climate responses.
      PubDate: 2017-09-18T06:16:22.304062-05:
      DOI: 10.1111/1365-2745.12837
       
  • Multiple factors modulate tree growth complementarity in Central European
           mixed forests
    • Authors: Marco Mina; Markus O. Huber, David I. Forrester, Esther Thürig, Brigitte Rohner
      Abstract: Mixed species forests can often be more productive and deliver higher levels of ecosystem services and functions than monocultures. However, complementarity effects for any given tree species are difficult to generalize because they can vary greatly along gradients of climatic conditions and resource availability. Identifying the conditions where species diversity can positively influence productivity is crucial. To date, few studies have examined how growth complementarity across species and mixture types is modulated by stand and environmental factors, and fewer have considered more than one or two factors.We investigated how complementarity effects for several major Central European tree species change with climatic and edaphic conditions, and with stand structural characteristics, including species composition. We used data from the Swiss National Forest Inventory, which is based on 3,231 plots of pure and mixed stands (19 mixture types) across a broad environmental gradient, to test (i) how mixing effects change depending on the identity of the admixed species and (ii) if complementarity consistently increases when environmental conditions become harsher.The magnitude, whether positive or negative, of complementarity increased with increasing stand density and stand developmental stage, but no general pattern could be identified across mixture types. Complementarity for many species increased as drought intensity and temperature increased, but not for all species and mixture types. While soil conditions, nitrogen and site topography influenced complementarity for many species, there was no general pattern (increases and decreases were observed).Synthesis. Our study indicates that complementarity varies strongly with stand density and stand development as well as with topographic, climatic and soil conditions. This emphasizes the need to account for site-dependent conditions when exploring mixture effects in relation to forest productivity. We found that under certain conditions (i.e. increasing drought, higher temperature), mixed forests can promote individual tree growth in Central European temperate forests. However, careful assessments depending on the species composing the stands are required under changing resource availability as well as under different levels of stand density and development.Complementarity effects for the main tree species growing in Central European mixed forests vary strongly with stand density and stand development as well as with topographic, climatic and soil conditions. This emphasizes the need to account for site-dependent conditions when exploring mixture effects in relation to forest productivity. Under certain conditions (i.e. increasing drought, higher temperature), mixed forests can promote individual tree growth but careful assessments depending on the species composing the stands are required under changing resource availability as well as under different levels of stand density and development.
      PubDate: 2017-09-14T05:10:37.202354-05:
      DOI: 10.1111/1365-2745.12846
       
  • Persisting in defaunated landscapes: Reduced plant population connectivity
           after seed dispersal collapse
    • Authors: Néstor Pérez-Méndez; Pedro Jordano, Alfredo Valido
      Abstract: Defaunation of large-bodied frugivores could be causing severe losses of crucial ecosystem functions such as seed dispersal. The immediate ecological consequences may include alteration or even collapse of seed-mediated gene flow affecting plant population connectivity, with impacts on the regional scale distribution of genetic variation. Yet, these far-reaching consequences of defaunation remain understudied.Here, we tested whether human-induced defaunation of the Canarian frugivorous lizards (Gallotia, Lacertidae) altered within-island population connectivity and the amount and large-scale distribution of genetic variation of Neochamaelea pulverulenta (Rutaceae), which relies exclusively on these lizards for seed dispersal. Our study system defines a lizard downsizing gradient with three contrasted ecological scenarios (islands) with relatively optimal (Gran Canaria; large-sized lizards), suboptimal (Tenerife; medium) and collapsed seed dispersal processes (La Gomera; small). We extensively sampled individual plant genotypes from 80 populations spanning the full geographical range of the plant to examine their genetic diversity, population-genetic network topologies, and the patterns of isolation both by distance (IBD) and resistance (IBR) across these three ecological scenarios.Plant genetic diversity appeared unaffected by defaunation-mediated downsizing of frugivorous lizards. However, we found a reduced overall plant population connectivity together with an increased isolation by distance within the most defaunated islands (La Gomera and, to a lesser extent, Tenerife) when compared with the scenario preserving the functionality of lizard-mediated seed dispersal (Gran Canaria). The results, with a significant effect of lizard downsizing, were robust when controlling for biotic/abiotic differences among the three islands by means of isolation by resistance models (IBR).Synthesis. Our results provide valuable insights into the far-reaching consequences of the deterioration of mutualisms on plant population dynamics over very large spatial scales. Conservation of large-bodied frugivores is, thus, essential because their irreplaceable mutualistic dispersal services maintain an extensive movement of seeds across the landscape, crucial for maintaining the genetic cohesiveness of metapopulations and the adaptive potential of plant species across their entire geographical range.Our results provide valuable insights into the far-reaching consequences of the deterioration of mutualisms on plant population dynamics over very large spatial scales. Conservation of large-bodied frugivores is, thus, essential because their irreplaceable mutualistic dispersal services maintain an extensive movement of seeds across the landscape, crucial for maintaining the genetic cohesiveness of metapopulations and the adaptive potential of plant species across their entire geographical range.
      PubDate: 2017-09-12T06:07:06.129359-05:
      DOI: 10.1111/1365-2745.12848
       
  • Breakdown of a geographic cline explains high performance of introduced
           populations of a weedy invader
    • Authors: Stacy B. Endriss; Christina Alba, Andrew P. Norton, Petr Pyšek, Ruth A. Hufbauer
      Abstract: What drives the evolution of increased growth and fecundity in plants introduced to a novel range is not well understood.We investigate between-range differences in performance for Verbascum thapsus, a weedy invader known to grow larger in its introduced than native range. Specifically, we question whether adaptation to herbivory or climate best explains increased performance of introduced populations.We grew 14 native and 22 introduced populations of V. thapsus in two common garden locations: near Prague, Czech Republic (native range) and in Colorado, USA (introduced range). By removing herbivores from half of the plants within each garden we tested the prediction of the evolution of increased competitive ability (EICA) hypothesis: increased performance is driven by an evolutionary shift of resources away from defence against herbivory towards growth and reproduction. We then investigated whether genetically based clines in performance are expressed along climate gradients within both the native and introduced ranges.On average, seeds produce larger rosettes when collected from the introduced vs. native range. While this evolution of increased growth in introduced populations in part matches the prediction of EICA, climate, not herbivory, best explains this between-range difference. Specifically, seeds collected from the native range produce smaller rosettes as the climate of origin becomes cooler and drier, while there is no cline in performance in rosettes grown from seed collected from the introduced range, which are large regardless of climate of origin. Thus, a climate-based cline within the native range best explains lower average performance of native compared to introduced populations.Synthesis. The breakdown in a potentially adaptive cline emphasizes the need to more closely investigate the evolutionary processes that shape geographic structuring (or its absence) within the introduced range. In addition, EICA is not universally applicable to all invasion scenarios, and our findings underscore the importance of testing the underlying assumptions alongside the predictions of this hypothesis.The breakdown of a cline in performance along climate gradients, not adaptation to herbivory, best explains high performance of introduced as compared to native populations of a weedy invader. Our findings emphasize the need to: (1) test the underlying assumptions alongside the predictions of EICA, and (2) further investigate processes shaping geographic structuring (or its absence) within the introduced range.
      PubDate: 2017-09-11T10:25:56.521298-05:
      DOI: 10.1111/1365-2745.12845
       
  • Soil biotic quality lacks spatial structure and is positively associated
           with fertility in a northern grassland
    • Authors: Pierre-Luc Chagnon; Charlotte Brown, Gisela C. Stotz, James F. Cahill
      Abstract: When placing roots in the soil, plants integrate information about soil nutrients, plant neighbours and beneficial/detrimental soil organisms. While the fine-scale spatial heterogeneity in soil nutrients and plant neighbours have been described previously, virtually nothing is known about the spatial structure in soil biotic quality (measured here as a soil Biota-Induced plant Growth Response, or BIGR), or its correlation with nutrients or neighbours. Such correlations could imply trade-offs in root placement decisions.Theory would predict that soil BIGR is (1) negatively related to soil fertility and (2) associated with plant community structure, such that plants influence soil biota (and vice versa) through plant–soil feedbacks. We would also expect that since plants have species-specific impacts on soil organisms, spatially homogeneous plant communities should also homogenize soil BIGR.Here, we test these hypotheses in a semi-arid grassland by (1) characterizing the spatial structure of soil BIGR at a scale experienced by an individual plant and (2) correlating it to soil abiotic properties and plant community structure. We do so in two types of plant communities: (1) low-diversity patches dominated by an invasive grass (Bromus inermis Leyss.) and (2) patches covered mostly by native vegetation, with the expectation that dominance by Bromus would homogenize soil BIGR.Soil BIGR was spatially heterogeneous, but not autocorrelated. This was true in both vegetation types (Bromus-invaded vs. native patches). Conversely, soil abiotic properties and plant community structure were frequently spatially autocorrelated at similar scales. Also, contrary to many studies, we found a positive correlation between soil BIGR and soil fertility. Soil BIGR was also associated with plant community structure.Synthesis. The positive correlation between soil BIGR and some soil nutrient levels suggests that plants do not necessarily trade-off between foraging for nutrients vs. biotic interactions: nutritional cues could rather indicate the presence of beneficial soil biota. Moreover, the spatial structure in plant communities, coupled with their correlation with soil BIGR, jointly suggest that plant–soil feedbacks operate at local scales in the field: this has been identified in modelling studies as an important driver of plant coexistence.The positive correlation between soil BIGR and some soil nutrient levels suggests that plants do not necessarily trade-off between foraging for nutrients vs. biotic interactions: nutritional cues could rather indicate the presence of beneficial soil biota. Moreover, the spatial structure in plant communities, coupled with their correlation with soil BIGR, jointly suggest that plant–soil feedbacks operate at local scales in the field: this has been identified in modelling studies as an important driver of plant coexistence.
      PubDate: 2017-09-11T09:47:07.953609-05:
      DOI: 10.1111/1365-2745.12844
       
  • Soil-mediated filtering organizes tree assemblages in regenerating
           tropical forests
    • Authors: Bruno Ximenes Pinho; Felipe Pimentel Lopes Melo, Víctor Arroyo-Rodríguez, Simon Pierce, Madelon Lohbeck, Marcelo Tabarelli
      Abstract: Secondary forests are increasingly dominant in human-modified tropical landscapes, but the drivers of forest recovery remain poorly understood. Soil conditions influence plant community composition, and are expected to change over a gradient of succession. However, the role of soil conditions as an environmental filter driving community assembly during forest succession has rarely been explicitly assessed.We evaluated the role of stand basal area and soil conditions on community assembly and its consequences for community functional properties along a chronosequence of Atlantic forest regeneration following sugar cane cultivation. Specifically, we tested whether community functional properties are related to stand basal area, soil fertility and soil moisture. Our expectations were that edaphic environmental filters play an increasingly important role along secondary succession by increasing functional trait convergence towards more conservative attributes.We sampled soil and woody vegetation features across 15 second-growth (3–30 years) and 11 old-growth forest plots (300 m2 each). We recorded tree functional traits related to resource-use strategies (specific leaf area, SLA; leaf dry matter content, LDMC; leaf area, LA; leaf thickness, LT; and leaf succulence, LS) and calculated community functional properties using the community-weighted mean (CWM) of each trait and the functional dispersion (FDis) of each trait separately and all traits together.With exception of LA, all leaf traits were strongly associated with stand basal area; LDMC and SLA increased, while LT and LS decreased with forest development. Such changes in LDMC, LT and LS were also related to the decrease in soil nutrient availability and pH along succession, while soil moisture was weakly related to community functional properties. Considering all traits, as well as leaf thickness and succulence separately, FDis strongly decreased with increasing basal area and decreasing soil fertility along forest succession, presenting the lowest values in old-growth forests.Synthesis. Our findings suggest that tropical forest regeneration may be a deterministic process shaped by soil conditions. Soil fertility operates as a key filter causing functional convergence towards more conservative resource-use strategies, such as leaves with higher leaf dry matter content.Our findings suggest that tropical forest regeneration may be a deterministic process shaped by soil conditions. Soil fertility operates as a key filter causing functional convergence towards more conservative resource-use strategies, such as leaves with higher leaf dry matter content.
      PubDate: 2017-09-04T05:22:28.665321-05:
      DOI: 10.1111/1365-2745.12843
       
  • Elevational transplantation suggests different responses of African
           submontane and savanna plants to climate warming
    • Authors: Andreas Ensslin; Neduvoto P. Mollel, Andreas Hemp, Markus Fischer
      Abstract: Despite strong climate change in the tropics, little is known about the responses of tropical plants to changing environments. Moreover, while variation in responses to climate change across plant functional groups may help to predict future vegetation dynamics, tropical multi-species studies are missing.To study plant responses to changes in temperature, we compared the survival, growth and reproduction of 101 herbaceous species originating from the savanna and the submontane vegetation zones in two experimental gardens representing the climate of both zones at Kilimanjaro, Tanzania. Additionally, we tested whether plant functional groups, such as annuals and perennials, shade-tolerant and shade-intolerant species, grasses and forbs, and natives and exotics differ in their responses to transplantation.We show that the submontane species in the lower Kilimanjaro area clearly prefer the cooler submontane temperature in terms of survival, growth and reproduction, while savanna plants can grow equally well under both, the submontane and the savanna temperature regimes. This suggests that tropical submontane plants will likely face severe challenges with future climate warming and that the upper distributional limit of savanna plants may be due to biotic interactions rather than to climate. Moreover, we found different responses of grasses and forbs, and natives and exotics to transplantation irrespective of their origin, underlining the importance of considering plant functional groups in climate change research.Synthesis. We demonstrate different responses of tropical submontane and savanna plants to experimental temperature variation. Together with the observed differences between important functional plant groups, this leads us to suggest that strong future changes in vegetation composition on African tropical mountains are likely.Little is known about the responses of tropical plants to climate warming. By transplanting 101 submontane and savanna species to two experimental gardens on Kilimanjaro, we demonstrate that submontane plants are strongly challenged by increased temperatures, while savanna plants can grow equally well under both temperature regimes. We suggest that strong future changes in vegetation composition on African mountains are likely.
      PubDate: 2017-09-04T05:22:07.131537-05:
      DOI: 10.1111/1365-2745.12842
       
  • Fatal attraction of non-vector impairs fitness of manipulating plant virus
    • Authors: Yesenia Ithaí Ángeles-López; Rafael Rivera-Bustamante, Martin Heil
      Abstract: Host manipulation refers to the expression of a host phenotype that is partly under the genetic control of a parasite. This phenomenon can enhance parasite transmission rates and is responsible for biological marvels such as “Zombie-ants” and the “fatal attraction” of Toxoplasma-infected rodents to their feline predators. Such host manipulation has evolved in all major phylogenetic lineages of parasites and is assumed to enhance the fitness of the parasite.However, the capacity to manipulate is not ubiquitous; that is, many clades of parasites comprise manipulating and non-manipulating species. This pattern leads to the prediction of costs that select against the evolution of manipulation, but this has been difficult to show empirically.In the present study, we used a tripartitate system consisting of chili (Capsicum annuum) plants infected with Pepper golden mosaic virus and colonized by non-vector whiteflies (Trialeurodes vaporariorum), to study the effects on viral load when a non-vector herbivore feeds on the infected plants.We observed that virus-infected plants emitted odours that attracted adult whiteflies, contained three times more amino acids in the phloem than mock-inoculated controls and supported higher whitefly reproduction as compared to controls. However, viral load decreased almost 100-fold in whitefly-carrying plants, which was associated with a depletion of phloem amino acids.Synthesis. We show that a plant virus can suffer from a reduced within-host reproduction rate when virus-induced alterations of the plant cause a “fatal attraction” of a non-vector insect that exploits the altered plant phenotype at its own benefits. The resulting fitness costs might represent a force that can select against the evolution of host manipulation by parasites.(I) Whiteflies use volatile organic compounds (VOCs) to choose chili plants that infected with the geminivirus, PepGMV,for feeding and oviposition, because these plants represent better hosts due to an increased content of amino acids in their phloem. This ‘fatal attraction’ of a non-vector can cause a significant fitness cost for the virus, because (II) the presence of ovipositing whiteflies and of nymphs has a strong negative effect on viral load in the plants.
      PubDate: 2017-09-04T05:21:56.324244-05:
      DOI: 10.1111/1365-2745.12838
       
  • Foliar uptake of nitrogen from ant faecal droplets: An overlooked service
           to ant-plants
    • Authors: Christian Pinkalski; Karl-Martin V. Jensen, Christian Damgaard, Joachim Offenberg
      Abstract: Nutrient supplies to plants from ants are well known from specialised myrmecophytic symbioses and from plants growing in soil close to ant nests. However, above-ground nutrient pathways may play a largely unrecognised role also in less specialised ant–plant interactions—the numerous facultative relationships, where ants forage on plants.In a laboratory experiment, weaver ants (Oecophylla smaragdina) were confined to the canopies of coffee (Coffea arabica) seedlings, excluding any ant-to-plant transfer of nutrients via the soil strata. When ants were fed 15N-labelled glycine and subsequently deposited faecal droplets on the seedlings, coffee leaves showed increased levels of 15N and total nitrogen compared to control plants without ants. This was evident for both exposed leaves and leaves covered in plastic bags (i.e. not directly exposed to ants). Thus, nitrogen from ant excretions was absorbed through the coffee leaves, and subsequently, translocated within the plants and possibly leading to the observed higher shoot/root (wet weight) ratios observed on ant-plants compared to controls.Synthesis. These results reveal an undescribed foliar uptake of ant-provided nutrients. If this is a general mechanism, a vast amount of ant–plant interactions involves fertilisation. Foliar fertilisation by ants may be an important steady benefit to plants, which has driven the evolution of ant–plant mutualisms in parallel with the well-recognised but probably more fluctuating benefit from herbivore protection. Given the world-wide abundance of plant canopies foraged by ants, this nutrient pathway may be of high ecological significance.These results reveal foliar uptake of ant-provided nutrients. If this is a general mechanism, a vast amount of ant–plant interactions involves fertilisation. Foliar fertilisation by ants may be an important steady benefit to plants, which has driven the evolution of ant–plant mutualisms in parallel with the well-recognised but probably more fluctuating benefit from herbivore protection. Given the world-wide abundance of plant canopies foraged by ants, this nutrient pathway may be of high ecological significance.
      PubDate: 2017-08-31T03:04:29.377311-05:
      DOI: 10.1111/1365-2745.12841
       
  • The role of species pools in determining species diversity in spatially
           heterogeneous communities
    • Authors: Ronen Ron; Ori Fragman-Sapir, Ronen Kadmon
      Abstract: The “habitat-specific species pool hypothesis” proposes that differences between habitats in the sizes of their species pools are the main drivers of diversity responses to habitat heterogeneity. Empirical tests of this hypothesis are not trivial as species might be missing from ecologically suitable habitats due to limited dispersal, while others may occur in unsuitable habitats by means of source–sink dynamics and mass effect.We tested the habitat-specific species pool hypothesis in a local, environmentally heterogeneous community of annual plants using a novel “ecological selection” experiment. Mixtures of seeds representing the whole community were sown in each habitat, and the emerging species were exposed to six generations of selection by environmental filtering and competition while being blocked from dispersal. A comparison of the total number of species that were able to survive in each habitat (i.e. to pass the selection test) with data on species richness in the natural community allowed us to test the degree to which observed differences in species richness between habitats could be explained by differences in the sizes of the respective species pools.Results supported the species pool hypothesis, showing that differences in the sizes of the habitat-specific species pools were important in determining diversity responses to habitat heterogeneity. Moreover, species richness showed a unimodal response to local-scale gradients in habitat productivity, and this response could be attributed to underlying differences in species pool sizes. Both results were robust to properties of the data and the method of analysis.Synthesis. Our results provide a strong experimental evidence that differences in the sizes of habitat-specific species pools might be important in shaping the diversity of local communities. Future theoretical and empirical studies in community ecology should explore the potential sources and implications of such differences.The ‘habitat-specific species pool hypothesis’ proposes that differences between habitats in the sizes of their species pools are important in determining diversity responses to habitat heterogeneity. We tested this hypothesis using a unique ‘ecological selection’ experiment in a system of Mediterranean annual plants. Results show that differences in the sizes of habitat-specific species pools are the main derivers of diversity responses to local heterogeneity in habitat conditions and that such differences also explain the unimodal response of the study communities to gradients in habitat productivity.
      PubDate: 2017-08-14T04:28:10.7998-05:00
      DOI: 10.1111/1365-2745.12840
       
  • Species-specific flowering cues among general flowering Shorea species at
           the Pasoh Research Forest, Malaysia
    • Authors: Yu-Yun Chen; Akiko Satake, I-Fang Sun, Yoshiko Kosugi, Makoto Tani, Shinya Numata, Stephen P. Hubbell, Christine Fletcher, Md. Noor Nur Supardi, S. Joseph Wright
      Abstract: In a unique phenomenon restricted to the ever wet forests of Southeast Asia, hundreds of species from dozens of plant families reproduce synchronously at irregular, multi-year intervals. The proximate environmental cues that synchronize these general flowering events have not been evaluated systematically because there have been no long-term, high temporal resolution, species-level records from the region.We present 13 years of weekly flowering records for five Shorea species as well as daily temperature and rainfall records from the Pasoh Forest Reserve, Peninsular Malaysia. We constructed models to evaluate hypothesized relationships between flowering and cool temperature, drought, and additive and synergistic effects of cool temperature and drought for each species. Model parameters include periods of time for floral cue accumulation and flower development and temperature and/or rainfall thresholds required for floral initiation. Parameters estimated using flowering observations from 2001 to 2011 were used to forecast flowering for 2011–2014.We show that drought and cool temperatures acting synergistically best explain the timing of flowering events for all Shorea species in the section Mutica and forecast the largest general flowering event accurately. Periods estimated for signal accumulation ranged from 54 to 90 days among species. Periods estimated for flowers to develop ranged between 43 and 96 days and closely followed the interspecific sequence of flowering in the Shorea species. Drought and temperature thresholds also varied among species, with Shorea maxwelliana requiring the most severe drought and Shorea leprosula the lowest temperatures.Synthesis. Our results indicate that cool temperatures and low rainfall occurring on seasonal time-scales of about 2–3 months rather than brief cold snaps or brief droughts best explain general flowering in Shorea species at the Pasoh Forest Reserve. Low rainfall is equally likely in winter (December–February) and summer (July–August) and cool temperatures are most likely in winter at Pasoh, which explains why general flowering events are restricted to spring and fall, with more frequent and stronger flowering in spring. In addition, species-specific sensitivity to environmental cues suggests that future climate change will have differential impacts on the frequency of reproduction, with potential consequences for regeneration of these dominant species of lowland tropical forests.We present 13 years of flowering records for five Shorea species as well as daily temperature and rainfall records from the Pasoh Forest Reserve, Peninsular Malaysia. We show that drought and cool temperatures acting synergistically best explain the timing of flowering events and forecast the largest general flowering event accurately.
      PubDate: 2017-08-14T04:28:00.846035-05:
      DOI: 10.1111/1365-2745.12836
       
  • Priority effects caused by plant order of arrival affect below-ground
           productivity
    • Authors: Emanuela W. A. Weidlich; Philipp Gillhaussen, Johannes F. J. Max, Benjamin M. Delory, Nicolai D. Jablonowski, Uwe Rascher, Vicky M. Temperton
      Abstract: Plant species that arrive first in the system can affect assembly (priority effects). However, effects of order of arrival of different plant functional groups (PFGs) on root development have not yet been investigated under field conditions.We measured standing and fine root length density in the first and third year of a grassland field experiment. We wanted to know if manipulating PFG order of arrival would affect root development, and if priority effects are modulated by soil type.Sowing legumes first created a priority effect that was found in the first and third year, with a lower standing root length density in this treatment, even though the plant community composition was different in each of the studied years. Fine root length density was not affected by order of arrival, but changed according to the soil type.Synthesis. We found strong evidence that sowing legumes first created a priority effect below-ground that was found in the first and third year of this field experiment, even though the functional group dominance was different in each of the studied years.We investigated if manipulating the order of arrival of different plant functional groups (PFGs) would affect root development in a grassland field experiment. Sowing legumes first created a priority effect below-ground (lower root length) that was found in the first and third year of this field experiment, even though the functional group dominance was different in each of the studied years.
      PubDate: 2017-08-14T04:27:44.204417-05:
      DOI: 10.1111/1365-2745.12829
       
  • Overyielding in young tree plantations is driven by local complementarity
           and selection effects related to shade tolerance
    • Authors: Thomas Van de Peer; Kris Verheyen, Quentin Ponette, Nuri N. Setiawan, Bart Muys
      Abstract: Overyielding in mixed-species forests has been demonstrated in a vast body of literature, and the focus of functional biodiversity research is now shifting towards a mechanistic understanding of these observations.We explored diversity–productivity relationships at two sites of a large-scale tree diversity experiment, with harsh (Ged) and benign (Zed) environmental conditions for plantation establishment. Additive partitioning methodologies were adopted to detect phenomenological patterns in the productivity data, and the trait structure of mixed communities was used to advance insights into compositional effects.After 6 years of plantation development, biomass productivity was significantly higher in mixtures compared to the monocultures of component species. We observed that processes operated through direct tree–tree interactions, as the diversity signal disappeared where trees in mixed stands were surrounded by conspecific neighbours only. This result is particularly relevant for mixed-species plantation systems, as trees are commonly planted in monospecific patches to simplify management.Partitioning unveiled strong selection effects at both plantation sites. However, at the harsh Ged-site this was caused by competitive dominance of species with fast young growth, whereas at the benign Zed-site, species with slow young growth improved their performances but not at the expense of others (i.e. trait-dependent complementarity). Species tolerance to shading is an influential trait for predicting biodiversity effects, with community-weighted means in shade tolerance mediating dominance effects (Ged) and functional diversity in shade tolerance mediating (trait-dependent) complementarity effects (Zed).Synthesis. This study highlights that biodiversity effects in young tree plantations could be explained by the functional composition of mixed communities, with a key role for species levels of shade tolerance. As contrasting results between plantation sites were observed, future research should target the context-dependency of diversity–productivity relationships.This study highlights that biodiversity effects in young tree plantations could be explained by the functional composition of mixed communities, with a key role for species levels of shade tolerance. As contrasting results between plantation sites were observed, future research should target the context-dependency of diversity–productivity relationships.
      PubDate: 2017-08-14T04:27:37.870781-05:
      DOI: 10.1111/1365-2745.12839
       
  • The effects of climate warming and disturbance on the colonization
           potential of ornamental alien plant species
    • Authors: Emily Haeuser; Wayne Dawson, Mark Kleunen
      Abstract: 1.A large number of alien plant species have been introduced as ornamental garden plants to Europe, but relatively few have become invasive. Low climatic suitability may be limiting the current invasion potential of many alien ornamental species. However, with ongoing disturbance and climate change, this barrier may be reduced for some species.2.Here we tested how colonization ability (a prerequisite for invasion) of frequently planted alien ornamentals depends on disturbance and heating, and on their species characteristics. We sowed seeds of 37 non-naturalized alien herbaceous garden-plant species into native grassland plots with and without disturbance, and with and without infrared heating lamps. To assess whether their responses differ from those within the regional wild flora, we also sowed 14 native species and 12 naturalized alien species. During two years, we assessed the likelihoods of germination, first-year survival, second-year survival and flowering of these 63 study species.3.The heating treatment, which also reduced soil moisture, decreased all measures of colonization success, but more so for sown native species than for the non-naturalized and naturalized alien ones. The disturbance treatment increased colonization success, and because heating decreased productivity of the undisturbed grassland plots, it also increased invasibility of these plots. Average colonization success of non-naturalized aliens was reduced by heating, but some species were not affected or performed even better with heating, particularly those with an annual life span and a high seed mass. Winter hardiness improved colonization ability of non-naturalized aliens, but this advantage was reduced in the heated plots.4.Synthesis. Disturbance increased and heating decreased the absolute colonization success of most of the 63 species sown. However, heating had stronger adverse effects on the resident grassland and sown native species than either type of sown alien species. Together, these results suggest that some alien plants may have greater colonization success relative to native plants under a warmer climate.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-24T08:00:32.525083-05:
      DOI: 10.1111/1365-2745.12798
       
  • Climate and competition effects on tree growth in Rocky Mountain forests
    • Authors: Arne Buechling; Patrick H. Martin, Charles D. Canham
      Abstract: 1.Climate is widely assumed to influence physiological and demographic processes in trees, and hence forest composition, biomass and range limits. Growth in trees is an important barometer of climate change impacts on forests as growth is highly correlated with other demographic processes including tree mortality and fecundity.2.We investigated the main drivers of diameter growth for five common tree species occurring in the Rocky Mountains of the western United States using non-linear regression methods. We quantified growth at the individual tree level from tree core samples collected across broad environmental gradients. We estimated the effects of both climate variation and biotic interactions on growth processes and tested for evidence that disjunct populations of a species respond differentially to climate.3.Relationships between tree growth and climate varied by species and location. Growth in all species responded positively to increases in annual moisture up to a threshold level. Modest linear responses to temperature, both positive and negative, were observed at many sites. However, model results also revealed evidence for differentiated responses to local site conditions in all species. In severe environments in particular, growth responses varied non-linearly with temperature. For example, in northerly cold locations pronounced positive growth responses to increasing temperatures were observed. In warmer southerly climates, growth responses were unimodal, declining markedly above a threshold temperature level.4.Net effects from biotic interactions on diameter growth were negative for all study species. Evidence for facilitative effects was not detected. For some species, competitive effects more strongly influenced growth performance than climate. Competitive interactions also modified growth responses to climate to some degree.6.Synthesis. These analyses suggest that climate change will have complex, species specific effects on tree growth in the Rocky Mountains due to non-linear responses to climate, differentiated growth processes that vary by location and complex species interactions that impact growth and potentially modify responses to climate. Thus, robust model simulations of future growth responses to climate trends may need to integrate realistic scenarios of neighborhood effects as well as variability in tree performance attributed to differentiated populations.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-12T04:25:55.00461-05:0
      DOI: 10.1111/1365-2745.12782
       
  • Multi-scale drivers of community diversity and composition across tidal
           heights: an example on temperate seaweed communities
    • Authors: Marine Robuchon; Myriam Valero, Eric Thiébaut, Line Le Gall
      Abstract: 1.Despite recent advances in understanding community assembly processes, appreciating how these processes vary across multiple spatial scales and environmental gradients remains a crucial issue in ecology.2.This study aimed to disentangle the drivers of diversity and composition of seaweed communities through a gradient of spatial scales based on a hierarchical sampling design consisting of 19 sites distributed in four sectors along the Brittany coastline. Using randomised community matrices and Moran's eigenvector maps (MEMs), we compared i) the relative importance of deterministic and stochastic processes, ii) the environmental correlates of community composition and iii) the scale of variation in community composition for seaweed communities located at two different tidal heights.3.Processes shaping community patterns are expected to vary along a gradient of tidal heights. Therefore, we specifically examined the following hypotheses: the contribution of deterministic over stochastic processes as well as the relative importance of environmental filtering over biotic interactions should be enhanced for seaweed communities of the infralittoral fringe compared to subtidal ones, whereas dispersal of propagules in the water column should be more restricted resulting in finer-scale variation in community composition for seaweed communities of the infralittoral fringe compared to subtidal communities.4.Seaweed communities were largely shaped by deterministic processes, although the relative importance of deterministic processes was greater for communities of the infralittoral fringe than for subtidal communities. Sea surface temperature and geophysical variables were correlates of community composition at the two tidal heights; additionally, waves and current were correlated with the composition of the communities of the infralittoral fringe while kelp density was correlated with the composition of subtidal communities. Variation in community composition was observed at a finer scale for infralittoral fringe than for subtidal communities.Synthesis. Our results suggest that the relative importance of deterministic and stochastic processes in structuring seaweed communities varies across tidal heights. Furthermore, the MEMs framework highlights that the nature of environmental correlates and the spatial scale at which they were good correlates of community composition also vary across tidal heights and may therefore be useful to broaden our understanding of community assembly across vertical gradients.This article is protected by copyright. All rights reserved.
      PubDate: 2017-04-09T23:55:25.836747-05:
      DOI: 10.1111/1365-2745.12781
       
  • Interactions between rainfall, fire and herbivory drive resprouter vital
           rates in a semi-arid ecosystem
    • Authors: Katherine M. Giljohann; Michael A. McCarthy, David A. Keith, Luke T. Kelly, Mark G. Tozer, Tracey J. Regan
      Abstract: Global change is threatening ecosystems and biodiversity world-wide, creating a pressing need to understand how climate and disturbance regimes interact and influence the persistence of species. We quantify how three ecosystem drivers – rainfall, fire and herbivory – influence vital rates in the perennial resprouting graminoid, Triodia scariosa, a foundation species of semi-arid Australia.We used an 11-year dataset from a fire and herbivore exclosure experiment, to model flowering, post-fire recruitment and the post-fire survival of seedlings and resprouting plants. Regression modelling quantified the effect of rainfall, inter-fire interval, fire type (wildfire or prescribed fire), grazing by herbivores (native and feral) and an interaction between fire type and herbivory on T. scariosa populations.Rainfall, fire and herbivory had significant effects on post-fire recruitment and the survival of seedlings and resprouting plants, including strong interactions between these drivers. Herbivory following wildfire had a minor effect, but in years of below-average rainfall herbivory following prescribed fire had a large effect, reducing the survival of seedlings and resprouting plants by 20% and over 50% respectively, relative to post-fire survival under average rainfall conditions.Variation in rainfall underpinned significant variation in post-fire resprouting and seedling survival, thus we postulate rainfall primarily drives the dynamics of T. scariosa populations.Synthesis. This study highlights the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes can substantially alter population processes, even in perennial resprouting species. This work suggests that conservation of foundation species, such as T. scariosa, will benefit if fire management decisions are better integrated with inter-annual weather forecasts and herbivore management.Our study shows the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes substantially altered population processes in a perennial resprouting species. This suggests that conservation of foundation species will benefit if fire management decisions are better integrated with inter-annual weather forecasts and herbivore management. The photo was taken by David Keith at Tarawi Nature Reserve in 2013 and shows part of a herbivore exclosure at 7 years post-fire.
      PubDate: 2017-04-06T05:35:18.93946-05:0
      DOI: 10.1111/1365-2745.12768
       
  • The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N
           labelling study
    • Authors: Melissa A. Dawes; Patrick Schleppi, Frank Hagedorn
      Abstract: Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N-poor high-elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant-soil system and how warming influences these patterns, we applied a 15N label (15NH4Cl or 15N-glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4°C) at treeline in the Swiss Alps.Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was
      PubDate: 2017-04-04T15:55:23.148449-05:
      DOI: 10.1111/1365-2745.12780
       
  • Microbial communities in soil chronosequences with distinct parent
           material: the effect of soil pH and litter quality
    • Authors: Fernando D. Alfaro; Marlene Manzano, Pablo A. Marquet, Aurora Gaxiola
      Abstract: During soil development, bacteria and fungi can be differentially affected by changes in soil biogeochemistry. Since the chemistry of parent material affects soil pH, nutrient availability, and indirectly litter quality, we hypothesize that parent material has an important influence on microbial community patterns during long-term soil development.In this paper, we tested for the effect of parent material, as well as, soil and litter properties upon microbial community patterns in three c. 20 000-year-old semi-arid chronosequences developed on sedimentary and volcanic (i.e. Andesitic and Dacitic) soils in the Dry Puna of Bolivia. We evaluated microbial patterns by analysing the terminal restriction fragment length polymorphism from amplified bacterial 16S rRNA genes, and the fungal internal transcribed spacer region, and quantitative real-time polymerase chain reaction.Soil and litter characteristics differed significantly between the Sedimentary and volcanic chronosequences. In particular, soil pH was alkaline in all stages of the Sedimentary chronosequence; whereas it changed from alkaline to near neutral across stages in both volcanic chronosequences. Composition of bacterial communities changed across volcanic chronosequences, and this change was associated with a reduction in soil pH and increases in litter quality, whereas no differences were found in the Sedimentary chronosequence. Fungal community composition, in contrast, did not change across any chronosequence.Relative microbial abundance, expressed as the fungal:bacterial ratio, declined across stages of the Sedimentary chronosequence in association with decreases in TC and TP, whereas in the Andesitic chronosequence decreases in fungal:bacterial ratios were related with increases in litter quality and declines in soil pH.Synthesis. Our results show the importance of parent material in affecting bacterial and fungal communities during soil development. Further, in semi-arid chronosequences, fungal:bacterial ratios tend to decline given that soil pH in young soils is rather alkaline. Our results also are consistent with the general framework that highlights the importance of above-ground (i.e. litter quality) and below-ground (i.e. soil properties) in affecting microbial relative abundance and community composition during soil development.We tested the effect of parent material, as well as soil and litter properties, upon microbial community patterns in c. 20 000-year-old chronosequences of sedimentary and volcanic origin in the Dry Puna of Bolivia. We show that parent material is paramount in affecting soil pedogenesis and ecosystem dynamics via its effects upon soil pH, soil nutrient availability and litter quality, which in turn affects microbial abundance and composition.
      PubDate: 2017-04-04T03:45:59.613721-05:
      DOI: 10.1111/1365-2745.12766
       
  • Soil carbon response to woody plant encroachment: importance of spatial
           heterogeneity and deep soil storage
    • Authors: Yong Zhou; Thomas W. Boutton, X. Ben Wu
      Abstract: Recent global trends of increasing woody plant abundance in grass-dominated ecosystems may substantially enhance soil organic carbon (SOC) storage and could represent a strong carbon (C) sink in the terrestrial environment. However, few studies have quantitatively addressed the influence of spatial heterogeneity of vegetation and soil properties on SOC storage at the landscape scale. In addition, most studies assessing SOC response to woody encroachment consider only surface soils, and have not explicitly assessed the extent to which deeper portions of the soil profile may be sequestering C.We quantified the direction, magnitude and pattern of spatial heterogeneity of SOC in the upper 1·2 m of the profile following woody encroachment via spatially specific intensive soil sampling across a landscape in a subtropical savanna in the Rio Grande Plains, USA, that has undergone woody proliferation during the past century.Increased SOC accumulation following woody encroachment was observed to considerable depth, albeit at reduced magnitudes in deeper portions of the profile. Overall, woody clusters and groves accumulated 12·87 and 18·67 Mg C ha−1 more SOC compared to grasslands to a depth of 1·2 m.Woody encroachment significantly altered the pattern of spatial heterogeneity of SOC to a depth of 5 cm, with marginal effect at 5–15 cm, and no significant impact on soils below 15 cm. Fine root density explained greater variability of SOC in the upper 15 cm, while a combination of fine root density and soil clay content accounted for more of the variation in SOC in soils below 15 cm across this landscape.Synthesis. Substantial soil organic carbon sequestration can occur in deeper portions of the soil profile following woody encroachment. Furthermore, vegetation patterns and soil properties influenced the spatial heterogeneity and uncertainty of soil organic carbon in this landscape, highlighting the need for spatially specific sampling that can characterize this variability and enable scaling and modelling. Given the geographic extent of woody encroachment on a global scale, this undocumented deep soil carbon sequestration suggests this vegetation change may play a more significant role in regional and global carbon sequestration than previously thought.Woody plant encroachment into grasslands increased soil organic carbon (SOC) storage and influenced the spatial heterogeneity and uncertainty of SOC throughout the soil profile. In addition, much of the SOC accrual following woody encroachment was stored deep in the profile. Given the geographic extent of woody encroachment on a global scale, this undocumented deep soil C sequestration suggests this vegetation change may play a more significant role in regional and global C sequestration than previously thought.
      PubDate: 2017-04-03T07:50:44.37563-05:0
      DOI: 10.1111/1365-2745.12770
       
  • From pristine forests to high-altitude pastures: an ecological approach to
           prehistoric human impact on vegetation and landscapes in the western
           Italian Alps
    • Authors: Roberta Pini; Cesare Ravazzi, Luca Raiteri, Antonio Guerreschi, Lorenzo Castellano, Roberto Comolli
      Abstract: This paper addresses the origin and development of the oldest prehistoric pasture in the timberline ecotone known so far in the Alps and its relation to anthropogenic pressure and natural climate change.Palaeoecological and geochemical techniques were applied on the Crotte Basse mire stratigraphy (2365 m a.s.l, northwestern Italy) to describe changes in vegetation composition, forest biomass, land use and fertilization between c. 6400–1800 cal years bp.Subalpine forests dominated by Pinus cembra occurred at very high-altitude up to c. 5600 cal years bp, when a sharp contraction of woody vegetation took place. This major vegetation shift is matched by increasing charcoal input and markers of pastoral/grazing activities (pollen, dung spores and forms of phosphorus) in the sediment sequence in this small basin.Major phases of landscape change detected in our multiproxy record chronologically match intervals of cumulative probability density of 14C ages from nearby archaeological sites, suggesting that human activity was the factor leading to massive landscape change from the onset of the Copper Age (c. 5600 cal years bp). The change may have been reinforced by climate variability in the period 5700–5300 cal years bp.Sensitivity of woody species to fires was statistically explored (Appendix S1, Supporting Information), revealing negative reactions of P. cembra and Betula to frequent fire episodes and positive reactions of Alnus viridis and Juniperus. Fire episodes do not affect Larix dynamics.Synthesis. Mt. Fallère provides some of the oldest and consistent evidence so far available in the Alps for major anthropogenic pressure at the upper forest limit. As far back as 5600 cal years bp, high-elevation forest ecosystems were permanently disrupted and the alpine pastures were created. Palaeoecological data enable a clear distinction between a random and sporadic use of the alpine space, typical for Mesolithic and Neolithic societies, and an organized seasonal exploitation of natural resources, starting from the Copper Age onwards. The chronological comparison of independent climate proxies, palaeoecological information and pollen-based temperature reconstructions sheds light on the relationships between climate and humans since prehistoric times.This extensive and biodiverse cow pasture in the elevational belt of the western Italian Alps was suddenly installed at the Copper Age onset at the expenses of timberline forests. A 5600 years-long history of permanent herding and landscape management is narrated by the palaeoecological archive retrieved from a pond used for livestock watering.
      PubDate: 2017-04-03T02:31:18.828407-05:
      DOI: 10.1111/1365-2745.12767
       
  • Manipulating two olfactory cues causes a biological control beetle to
           shift to non-target plant species
    • Authors: Na Li; Shuang Li, Jin Ge, Meredith C. Schuman, Jia-Ning Wei, Rui-Yan Ma
      Abstract: 1.Olfactory cues can determine the host preferences of herbivorous insects, but their role in host shifting is unclear. Host specificity and the potential for host shifts are important criteria for screening and post-release evaluation of biological control agents for invasive plants. However, the role of olfactory cues in mediating host shifts in biological control agents is not well understood.2.To investigate the role of olfactory cues in host selection of a reportedly monophagous flea beetle (Agasicles hygrophila), an important biocontrol agent for invasive alligator weed (Alternanthera philoxeroides), we extracted and analyzed the volatiles produced by the host plant A. philoxeroides and the non-host plants A. sessilis, Beta vulgaris, and Amaranthus mangostanus. Moreover, we used electrophysiologcial techniques, behavioural bioassays and field trials to test the antennal responses and behavioural preferences of A. hygrophila to combinations of different plant volatiles and treatments, and pure compounds in different dosages and combinations.3.We show that A. hygrophila female beetles indeed use olfactory cues to select plants for feeding and oviposition and that the survivorship of larvae on the second preferred non-host plant A. sessilis, a close relative of the first preferred host plant A. philoxeroides, was over 75% in a field trail. Although female beetles responded to many volatile compounds from host and non-host plants, (E)-4,8-dimethyl-1,3,7- nonatriene (DMNT) positively encouraged the beetle's feeding and oviposition preferences, whereas (Z)-3-hexenol displayed repellent effect. Remarkably, complementation assays with (Z)-3-hexenol on host plant or DMNT on non-host plants significantly shifted A. hygrophila host preferences to non-host plants and resulted in oviposition and egg hatching on the non-host plant A. sessilis in field trials.4.Synthesis. We demonstrate an olfactory mechanism by which a specialized herbivorous beetle uses the ratio of two common plant volatiles, DMNT and (Z)-3-hexenol, to discriminate between its host and non-host plants in nature. This study highlights an important mechanism by which olfactory cues could lead to undesired host range expansion in biocontrol agent, thus representing an important warning of the potential for a host shift and development of invasiveness in a common biocontrol agent, the flea beetle.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-29T07:54:20.752819-05:
      DOI: 10.1111/1365-2745.12778
       
  • In the presence of specialist root and shoot herbivory, invasive-range
           Brassica nigra populations have stronger competitive effects than
           native-range populations
    • Authors: Ayub M.O. Oduor; Mark Kleunen, Marc Stift
      Abstract: 1.The evolution of increased competitive ability (EICA) hypothesis predicts that release from specialist herbivores enables invasive plants to evolve increased growth. The most powerful tests of EICA hypothesis are provided by approaches that simultaneously assess the effects of specialist herbivory and competitive interactions. However, such approaches are extremely rare, and hence how simultaneous release from root and shoot herbivory influence competitive ability of invasive plants remains little understood.2.Here, we tested whether invasive-range Brassica nigra plants have evolved increased competitive ability, and whether expression of competitive ability depends on separate and simultaneous effects of specialist root and shoot herbivory. To do this, we grew B. nigra plants from eight invasive-range and eight native-range populations in the presence versus absence of competition with a community of native plant species, and in the absence versus presence of separate and simultaneous damage by a specialist root herbivore (Delia radicum) and a specialist shoot herbivore (Plutella xylostella). Brassica nigra performance was assessed by measuring biomass production and flowering of individual B. nigra plants.3.In partial support of the EICA hypothesis, invasive-range B. nigra had greater flowering than native-range conspecifics in the absence of competition. However, contrary to a prediction of the EICA hypothesis, invasive-range B. nigra produced less aboveground biomass than native-range B.nigra in the absence of shoot herbivory and competition. Moreover, with simultaneous root and shoot herbivory, invasive-range B. nigra suppressed a competing community more strongly than native-range B. nigra did.4.Synthesis: Our results suggest that invasiveness may be driven by mechanisms other than increased individual size. Simultaneous root and shoot herbivory in the invasive range may enhance suppressive effects of introduced plant species that have not completely escaped herbivore damage in the introduced range.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-29T07:36:01.59134-05:0
      DOI: 10.1111/1365-2745.12779
       
  • Interspecific integration of trait dimensions at local scales: the plant
           phenotype as an integrated network
    • Authors: Julie Messier; Martin J. Lechowicz, Brian J. McGill, Cyrille Violle, Brian J. Enquist
      Abstract: Plant phenotypic diversity is shaped by the interplay of trade-offs and constraints in evolution. Closely integrated groups of traits (i.e. trait dimensions) are used to classify plant phenotypic diversity into plant strategies, but we do not know the degree of interdependence among trait dimensions. To assess how selection has shaped the phenotypic space, we examine whether trait dimensions are independent.We gathered data on saplings of 24 locally coexisting tree species in a temperate forest, and examined the correlation structure of 20 leaf, branch, stem and root traits. These traits fall into three well-established trait dimensions (the leaf economic spectrum, the wood spectrum and Corner's Rules) that characterize vital plant functions: resource acquisition, sap transport, mechanical support and canopy architecture. Using ordinations, network analyses and Mantel tests, we tested whether the sapling phenotype of these tree species is organized along independent trait dimensions.Across species, the sapling phenotype is not structured into clear trait dimensions. The trait relationships defining trait dimensions are either weak or absent and do not dominate the correlation structure of the sapling phenotype as a whole. Instead traits from the three commonly recognized trait dimensions are organized into an integrated trait network. The effect of phylogeny on trait correlations is minimal.Our results indicate that trait dimensions apparent in broad-based interspecific surveys do not hold up among locally coexisting species. Furthermore, architectural traits appear central to the phenotypic network, suggesting a pivotal role for branching architecture in linking resource acquisition, mechanical support and hydraulic functions.Synthesis. Our study indicates that local and global patterns of phenotypic integration differ and calls into question the use of trait dimensions at local scales. We propose that a network approach to assessing plant function more effectively reflects the multiple trade-offs and constraints shaping the phenotype in locally co-occurring species.Our study finds that globally defined trait dimensions are not independent (or even present) at a local scale. This calls into question the use of trait dimensions for local-scale ecology. We propose that a network approach to assessing plant function more effectively reflects the multiple trade-offs and constraints shaping the phenotype in locally co-occurring species.
      PubDate: 2017-03-27T05:12:15.333506-05:
      DOI: 10.1111/1365-2745.12755
       
  • Different response-effect trait relationships underlie contrasting
           responses to two chemical stressors
    • Authors: Christoph Mensens; Frederik De Laender, Colin R. Janssen, Koen Sabbe, Marleen De Troch
      Abstract: 1.Trait-based approaches evaluate ecosystem functioning under environmental change by relating traits predicting changes in species densities (response traits) to traits driving ecosystem functioning (effect traits). Stressors can however affect ecosystem functioning not only by altering species densities, but also by directly changing species effect traits.2.We first identified the response traits predicting the cell density of 18 marine benthic diatom strains along gradients of two chemical stressors (a pesticide and a metal, atrazine and copper). We then tested if response traits could predict stressor-induced changes in ecosystem functioning, i.e. changes in the effect traits driving the diatoms’ potential contribution to primary production, sediment stabilization and energy content in intertidal systems. Finally, we examined if changes in density and changes in ecosystem functioning were correlated, to assess whether species capable of growing under stressful conditions could maintain their contribution to ecosystem functioning.3.The relationship between response traits and stressor-induced changes in density and ecosystem functioning was different depending on stressor type: a set of intercorrelated morphological traits predicted changes in both density and ecosystem functioning under metal stress, with large cells being more stress-resistant. Changes in density and changes in ecosystem functioning were positively related: diatoms whose density was least affected by the metal were also able to sustain functioning under metal exposure.4.In contrast, the capacity for mixotrophic growth predicted changes in density, but not changes in ecosystem functioning under pesticide stress. Pesticide effects on density and on ecosystem functioning were negatively related for energy content and sediment stabilization, indicating a limited capacity of pesticide-tolerant diatoms to maintain their contribution to ecosystem functioning.5.Synthesis. Ecosystem functioning under stress can depend on whether the response traits driving changes in species densities also predict direct stress effects on the species’ contribution to functioning. Based on our results, we expect a disproportionate loss of functioning when traits driving species densities do not allow to maintain ecosystem functioning under stress.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-25T02:00:31.408079-05:
      DOI: 10.1111/1365-2745.12777
       
  • Soil biota suppress positive plant diversity effects on productivity at
           high but not low soil fertility
    • Authors: Shan Luo; Gerlinde B. De Deyn, Bin Jiang, Shixiao Yu
      Abstract: 1. Plant community productivity commonly increases with increasing plant diversity, which is explained by complementarity among plant species in resource utilization (complementarity effect), or by selection of particularly productive plant species in diverse plant communities (selection effect). Recent studies have also shown that soil biota can drive the positive plant diversity–productivity relationship by suppressing productivity more in low- than in high-diversity plant communities. However, much remains unknown about whether soil fertility plays a role in determining how soil biota affect plant diversity–productivity relationships.2.We hypothesized that under high soil fertility conditions, negative soil biota effects dominate, which reduces plant monoculture biomass more than that of high-diversity plant communities. Conversely, under low soil fertility conditions, we hypothesized positive soil biota effects dominate, which facilitates plant resource partitioning and enhances community-level biomass in high-diversity plant communities. Hence we expected positive plant diversity–community productivity relationships under low and high soil fertility conditions but caused by different mechanisms.3.We tested these hypotheses using woody seedlings and set up plant assemblages with four species richness levels (one, two, four and eight species), and grew them in sterilized and unsterilized (sterilized soil + living soil inoculum) soils at two nutrient levels (low vs. high fertility).4.We found that at high fertility negative soil biota effects dominated and suppressed plant community biomass more in high-diversity plant communities than in monocultures, resulting in reduced complementarity effects of diverse plant communities and a non-significant plant species richness–community biomass relationship in unsterilized soil. Whereas at low fertility soil biota had net neutral to positive effects on plant community biomass but the beneficial effects did not increase with increasing plant species richness. Instead, soil biota neutrally affected the positive plant species richness–community biomass relationship, presumably due to non-specific effects of beneficial soil biota.5.Synthesis. Soil biota and soil fertility interactively determine plant species richness–community biomass relationships. Moreover, soil biota modulate the complementary resource use among plant species. These findings suggest that environmental context plays an important role in determining whether and how soil biota generate the biodiversity–productivity relationship. Future studies would benefit from revealing the mechanisms underlying the interactive effects of soil biota, soil fertility, and plant diversity on ecosystem functioning.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-19T20:11:10.749153-05:
      DOI: 10.1111/1365-2745.12773
       
  • Phenological responsiveness to climate differs among four species of
           Quercus in North America
    • Authors: Katharine L. Gerst; Natalie L. Rossington, Susan J. Mazer
      Abstract: 1.The timing of the seasonal activity of organisms is a tractable indicator of climate change. Many studies in North America have investigated the role of temperature on the onset date of phenological transitions in temperate deciduous trees and found that the onset of leafing and flowering in numerous species has occurred earlier in recent years, apparently in response to higher temperatures in winter and spring.2.Few studies have examined the climatic and biogeographic drivers of phenological responses in water-limited ecosystems or explored inter-specific variation in responses of phenological metrics other than the timing of onset, such as the periodicity or duration of phenological activity.3.This study used phenological observations of four species of Quercus contributed to the USA National Phenology Network database from 2009-2014 to investigate how responses to climate (temperature and precipitation) and geographic location (latitude, longitude and elevation) varied among two western North American species (Q. agrifolia and Q. lobata) and two eastern and central North American species (Q. alba and Q. rubra).4.Within years, in species in the western, water-limited ecosystems, the phenological phases observed here (bud break, flowers or flower buds) tend to occur intermittently throughout the growing season, and each event is of longer duration than the same phenophases of the temperate-zone species, rendering a single onset date an incomplete metric with which to track responsiveness or to compare species. By contrast, the eastern/central U.S. species were phenologically more responsive than the western species to spatial and temporal variation in winter, spring, and fall precipitation and maximum temperature.5.Synthesis: Within and between regions these congeners exhibited a diversity of responses to seasonal temperature and precipitation. This indicates that for predictive model development it is critical to understand how each underlying driver influences species that are adapted to different climatic regimes. These results underscore the value of studying a range of phenological metrics and species from a variety of ecosystems to better predict phenological responses to short-term variation and to long-term change in climate.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-19T20:10:42.386321-05:
      DOI: 10.1111/1365-2745.12774
       
  • Invasive seaweeds transform habitat structure and increase biodiversity of
           associated species
    • Authors: Jennifer A. Dijkstra; Larry G. Harris, Kristen Mello, Amber Litterer, Christopher Wells, Colin Ware
      Abstract: The visual landscape of marine and terrestrial systems is changing as a result of anthropogenic factors. Often these shifts involve introduced species that are morphologically dissimilar to native species, creating a unique biogenic structure and habitat for associated species within the landscape. While community level changes as a result of introduced species have been documented in both terrestrial and marine systems, it is still unclear how long-term shifts in species composition will affect habitat complexity or its potential to influence the biodiversity of species that occur at the base of the food web.We analysed quadrat photos collected at several subtidal sites in the Gulf of Maine over a 30+ year period, and collected individual seaweed species to determine their complexity and the biodiversity of meso-invertebrates associated with each species.By coupling the relationship of 30+ years of shifts in seaweed assemblages, morphological structure of the seaweed assemblage, and their meso-invertebrates, we determined introduced seaweeds have increased by up to 90%, corresponding to a rise in two-dimensional (2D) structure, and a decline in canopy height of subtidal rocky habitats. The highly complex two-dimensional habitat provided by introduced filamentous red seaweeds supports 2 to 3 times more meso-invertebrate individuals and species that form the base of the food web than simpler forms of morphological habitat.Synthesis: The present study demonstrates a long-term shift in foundation species towards a dominance of invasive seaweeds that directly reduce canopy height and increase the 2D biogenic structure of the habitat. These introduced seaweeds harbour greater biodiversity of species found at the base of the food web than seaweeds with simpler forms such as the native kelp species. Such shifts in habitat structure will propagate to food-webs by influencing the structure of lower trophic level meso-invertebrates and indirectly upper trophic level species that feed on these invertebrates and use the seaweed structure as refuge.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-18T10:05:26.754573-05:
      DOI: 10.1111/1365-2745.12775
       
  • Expansion of deciduous tall shrubs but not evergreen dwarf shrubs
           inhibited by reindeer in Scandes mountain range
    • Authors: Tage Vowles; Bengt Gunnarsson, Ulf Molau, Thomas Hickler, Leif Klemedtsson, Robert G. Björk
      Abstract: One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.We revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long-term grazing effects and vegetation changes in response to increasing temperatures between 1995 and 2011, in two vegetation types (shrub heath and mountain birch forest).In the field layer at the shrub heath sites, evergreen dwarf shrubs had increased in cover from 26% to 49% but were unaffected by grazing. Deciduous dwarf and tall shrubs also showed significant, though smaller, increases over time. At the birch forest sites, the increase was similar for evergreen dwarf shrubs (20–48%) but deciduous tall shrubs did not show the same consistent increase over time as in the shrub heath.The cover and height of the shrub layer were significantly greater in exclosures at the shrub heath sites, but no significant treatment effects were found on species richness or diversity.July soil temperatures and growing season thawing degree days (TDD) were higher in exclosures at all but one site, and there was a significant negative correlation between mean shrub layer height and soil TDD at the shrub heath sites.Synthesis. This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures. However, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Although tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.
      PubDate: 2017-03-16T05:51:12.242457-05:
      DOI: 10.1111/1365-2745.12753
       
  • Plant traits, stoichiometry and microbes as drivers of decomposition in
           the rhizosphere in a temperate grassland
    • Authors: Yolima Carrillo; Colin Bell, Akihiro Koyama, Alberto Canarini, Claudia M. Boot, Matthew Wallenstein, Elise Pendall
      Abstract: 1.It is becoming increasingly clear that plant roots can impact the decomposition of existing soil C in the rhizosphere. Studies under controlled conditions suggest this impact may be plant-species dependent, but whether this is the case in natural conditions or what factors underlie this variation is mostly unknown.2.With a novel field-based isotopic approach combining 13C enriched glucose and BrdU additions, we compared in-situ C decomposition of added labile C and native soil C (priming) among eight semi-arid grassland species’ rhizospheres to investigate the factors driving inter-species variation. We examined the influence of several rhizosphere factors related to soil chemistry, microbial activity, microbial community, microbial stoichiometry, plant chemistry and root morphology.3.Plant species generated distinct microbial and chemical rhizosphere environments, which translated into differences in the direction, magnitude and temporal dynamics of the soil C priming. Soil C decomposition was positively related to soil C/P and soil N/P (via its influence on the bacterial community), which in turn were positively related to plant N/P. Plant C/N was also a significant factor via its negative influence on soil N/P. In contrast, the main direct predictors of labile C decomposition were microbial biomass, microbial C/N and the C degrading enzymes, which in turn were linked to root morphology and C chemistry.4.Synthesis. Within this community, plant species’ rhizospheres can vary in their susceptibility to C loss in response to changes in C availability. Soil stoichiometry, driven by plant chemical traits, appeared to be the strongest driver of priming. Our study suggests that shifts in plant communities involving increases in N relative to P have the greatest potential to lead to C loss. We provide evidence of root morphology and C chemistry as drivers of labile C processing in soil, a novel empirical contribution to our understanding of the role of plant traits belowground. The contrasting regulation of different pools of soil C suggest observations of the regulation of simple C compounds should not be extrapolated to the whole C pool. Our findings provide support for rhizosphere-driven mechanisms by which shifts in plant community composition could have implications on the ecosystem-level C balance.This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-10T09:12:07.627318-05:
      DOI: 10.1111/1365-2745.12772
       
  • Plant functional connectivity – integrating landscape structure and
           effective dispersal
    • Authors: Alistair G. Auffret; Yessica Rico, James M. Bullock, Danny A. P. Hooftman, Robin J. Pakeman, Merel B. Soons, Alberto Suárez-Esteban, Anna Traveset, Helene H. Wagner, Sara A. O. Cousins
      Abstract: Dispersal is essential for species to survive the threats of habitat destruction and climate change. Combining descriptions of dispersal ability with those of landscape structure, the concept of functional connectivity has been popular for understanding and predicting species’ spatial responses to environmental change.Following recent advances, the functional connectivity concept is now able to move beyond landscape structure to consider more explicitly how other external factors such as climate and resources affect species movement. We argue that these factors, in addition to a consideration of the complete dispersal process, are critical for an accurate understanding of functional connectivity for plant species in response to environmental change.We use recent advances in dispersal, landscape and molecular ecology to describe how a range of external factors can influence effective dispersal in plant species, and how the resulting functional connectivity can be assessed.Synthesis. We define plant functional connectivity as the effective dispersal of propagules or pollen among habitat patches in a landscape. Plant functional connectivity is determined by a combination of landscape structure, interactions between plant, environment and dispersal vectors, and the successful establishment of individuals. We hope that this consolidation of recent research will help focus future connectivity research and conservation.We define plant functional connectivity as the effective dispersal of propagules or pollen among habitat patches in a landscape. Plant functional connectivity is determined by a combination of landscape structure, interactions between plant, environment and dispersal vectors, and the successful establishment of individuals. We hope that our consolidation of recent research will help focus future connectivity research and conservation.
      PubDate: 2017-02-27T10:11:52.382619-05:
      DOI: 10.1111/1365-2745.12742
       
  • Do impacts of an invasive nitrogen-fixing shrub on Douglas-fir and its
           ectomycorrhizal mutualism change over time following invasion?
    • Authors: Sara Grove; Ingrid M. Parker, Karen A. Haubensak
      Abstract: 1.Impacts of invasive species may change in magnitude and even direction with invasion age. Impacts could increase as the population increases, individuals grow in size, and ecological changes accumulate.2.We used a chronosequence approach to characterize the development of soil impacts over time following the invasion of Cytisus scoparius, a widespread nitrogen-fixing shrub thought to limit reforestation success. In a greenhouse experiment, we evaluated how abundance of ectomycorrhizal fungi, Douglas-fir performance, and leaf nitrogen changed across a 3-31 year chronosequence of invasion. Each of the chronosequence sites were clearcuts where reforestation efforts were unsuccessful and where C. scoparius invaded. To estimate the contributions of the invasion separately from contributions of the accompanying disturbance, i.e. deforestation, we included soils from both invaded and uninvaded patches in each site of the chronosequence. In a complementary soil conditioning experiment, we examined the separate effects of host absence and invader presence on the mycorrhizal mutualism, leaf nitrogen, and seedling growth.3.Ectomycorrhizal colonization was lower in invaded soil, but this effect did not intensify with time. Despite the suppression of the mutualism, Douglas-fir grew larger in invaded soils. This positive response is likely due to nitrogen fertilization, a conclusion supported by higher concentrations of leaf nitrogen of Douglas-fir grown in invaded soils. While leaf N concentration increased with invasion duration, Douglas-fir survival and growth did not.Synthesis. Our findings suggest that soil impacts of an invader can develop rapidly and can be surprisingly stable over time. In such systems, recently invaded areas may be as difficult to restore as long invaded areas, especially where ectomycorrhizal fungi are important drivers of reforestation success. More chronosequence studies or long time series are needed to evaluate whether this is a general pattern.This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-24T14:10:24.306734-05:
      DOI: 10.1111/1365-2745.12764
       
  • Towards a trait-based ecology of wetland vegetation
    • Authors: Helen Moor; Håkan Rydin, Kristoffer Hylander, Mats B. Nilsson, Regina Lindborg, Jon Norberg
      Abstract: Functional traits mechanistically capture plant responses to environmental gradients as well as plant effects on ecosystem functioning. Yet most trait-based theory stems from terrestrial systems and extension to other habitats can provide new insights.Wetlands differ from terrestrial systems in conditions (e.g. soil water saturation, anoxia, pH extremes), plant adaptations (e.g. aerenchyma, clonality, ubiquity of bryophytes) and important processes (e.g. denitrification, peat accumulation, methane emission). Wetland plant adaptations and trait (co-)variation can be situated along major plant trait trade-off axes (e.g. the resource economics spectrum), but soil saturation represents a complex stress gradient beyond a simple extension of commonly studied water availability gradients.Traits that affect ecosystem functioning overlap with patterns in terrestrial systems. But wetland-specific traits that mediate plant effects on soil redox conditions, microbial communities and on water flow, as well as trait spectra of mosses, vary among wetland types.Synthesis. With increasing availability of quantitative plant traits a trait-based ecology of wetlands is emerging, with the potential to advance process-based understanding and prediction. We provide an interactive cause-and-effect framework that may guide research efforts to disentangle the multiple interacting processes involved in scaling from environmental conditions to ecosystem functioning via plant communities.With the increasing availability of quantitative plant traits a trait-based ecology of wetlands is emerging, with the potential to advance process-based understanding and prediction. We provide an interactive cause-and-effect framework that may guide research efforts to disentangle the multiple interacting processes involved in scaling from environmental conditions to ecosystem functioning via plant communities.
      PubDate: 2017-02-02T05:30:56.016069-05:
      DOI: 10.1111/1365-2745.12734
       
  • Long-term dynamics and impacts of plant invasions
    • Authors: Carla D'Antonio; S. Luke Flory
      Pages: 1459 - 1461
      Abstract: Hundreds of studies have evaluated the dynamics of plant invasions and their impacts on native plant communities and ecosystem functions, but most are limited in duration to only one or a few years. As such, we have a poor understanding of how invader dynamics and impacts change over time.This special feature presents six studies that use literature reviews, field studies and experiments to examine long-term patterns in invader effects on species, communities and ecosystems. All studies in the special feature focus on data collected over multiple years and two studies provide data that cover multiple decades.One study provides a review and framework for understanding how invaders impact plant–mycorrhiza mutualisms and two studies focus on long-term ecosystem changes in response to invasion and fire. The next two studies examine how invaders respond to successional change and climate conditions over time, and the final study shows that invaders can shift selection regimes and the evolutionary trajectory of native plant populations.Synthesis. Articles in this special feature demonstrate changes in the dynamics of invasive plant populations and their community and ecosystem impacts over time. Together they illustrate that findings from a snapshot in time may poorly describe years-long outcomes of invasions, and they highlight the need for long-term studies of biological invasions.
      PubDate: 2017-10-20T03:38:10.665965-05:
      DOI: 10.1111/1365-2745.12879
       
  • Ecosystem vs. community recovery 25 years after grass invasions and fire
           in a subtropical woodland
    • Authors: Carla M. D'Antonio; Stephanie G. Yelenik, Michelle C. Mack
      Pages: 1462 - 1474
      Abstract: Despite a large body of research documenting invasive plant impacts, few studies have followed individual invaded sites over decades to observe how they change, and none have contrasted how compositional impacts from invasion compare to ecosystem-process impacts over a multi-decadal time-scale.Using direct measurements of plant density and composition and of ecosystems processes, we evaluate how ecosystem structure, above-ground net primary production (ANPP), and above-ground and soil nutrient pools compare over 25 years since fire and C4 grass invasions disrupted seasonally dry Hawaiian woodlands. We compare structure and function between primary woodland that has never burned and is largely native species-dominated, with sites that had been the same woodland type but burned in alien-grass-fuelled fires in the 1970s and 1980s. The sites have not experienced fires since 1987.We report here that woody plant composition and structure continue to be dramatically changed by the initial invasions and fires that occurred 25 years ago and invaders continue to dominate in burned sites. This is reflected in continued low plant carbon pools in burned compared to unburned sites. Yet ANPP and N storage, which were dramatically lower in the initial decade after invasive-grass fuelled fires, have increased and are now indistinguishable from values measured in intact woodlands. Soil carbon pools were resilient to both invasion and fire initially and over time.Above-ground net primary production has recovered because of invasion of burned sites by a non-native N-fixing tree rather than because of recovery of native species. This invasive N-fixing tree is unlikely to return C storage of the invaded sites to those of unburned woodland because of its tissue and growth characteristics and its interactions with invasive grasses. It does not facilitate native species but rather promotes a persistent invasive grass/N-fixer savanna.Synthesis. We conclude that fire, an unusual disturbance in this system, has perpetuated the dominance of these sites by invasive species and that despite the dramatic recovery of above-ground net primary production and N pools, the ecosystem continues to be in a distinctly different state than the pre-fire, pre-Melinis community. Thus, despite the absence of further disturbance (fire), there is no evidence that succession towards the original ecosystem is occurring. The fact that N pools and above-ground net primary production recover because of a new invader (Morella faya), highlights the unpredictability of ecosystem trajectories in the face of altered regional species pools.We conclude that fire, an unusual disturbance in this system, has perpetuated the dominance of these sites by invasive species and that despite the dramatic recovery of above-ground net primary production and N pools, the ecosystem continues to be in a distinctly different state that the pre-fire, pre-Melinis community. Thus, despite the absence of further disturbance (fire), there is no evidence that succession towards the original ecosystem is occurring. The fact that N pools and above-ground net primary production recover because of a new invader (Morella faya), highlights the unpredictability of ecosystem trajectories in the face of altered regional species pools.
      PubDate: 2017-10-20T03:38:14.005454-05:
      DOI: 10.1111/1365-2745.12855
       
  • Effects of a non-native grass invasion decline over time
    • Authors: S. Luke Flory; Jonathan Bauer, Richard P. Phillips, Keith Clay
      Pages: 1475 - 1484
      Abstract: Most research on dynamics and impacts of plant invasions has evaluated patterns and effects over brief time periods (i.e.
      PubDate: 2017-10-20T03:38:18.733514-05:
      DOI: 10.1111/1365-2745.12850
       
  • Climate and rapid local adaptation as drivers of germination and seed bank
           dynamics of Alliaria petiolata (garlic mustard) in North America
    • Authors: Bernd Blossey; Victoria Nuzzo, Andrea Dávalos
      Pages: 1485 - 1495
      Abstract: Local differences in climate conditions may facilitate rapid evolutionary changes in introduced plants to optimize timing of germination or ability to survive in seed banks, which may constitute beneficial demographic adaptations during range expansions. Understanding differences in germination requirements and emergence patterns across a species’ range is critical for demographic modelling and potential invasive species control efforts.We assessed germination responses of Alliaria petiolata using seeds collected from 10 populations spanning much of the North American distribution of the species. We compared germination responses under different stratification regimes in a growth chamber over 2·5 years, and evaluated seedling emergence in a common garden in Ithaca, New York over 13 years. We further evaluated how climate overlap between Ithaca and original collection sites influenced emergence patterns.In the laboratory, germination of all populations was similar and highest at 4 °C stratification. Seeds exposed to sub-zero temperatures delayed germination and population responses were variable. In the common garden, seedlings from most populations emerged over 13 years, and emergence patterns were strongly influenced by population. Annual emergence was positively correlated with spring temperature and inversely correlated with number of spring days with minimum temperature below freezing. Climate overlap between the common garden and original collection location enhanced germination, but common garden climate conditions over the course of the 13-year experiment and population identity had greater explanatory power.Synthesis. Laboratory germination tests did not reflect seedling emergence under field conditions. After 150 years of residence time in North America, Alliaria petiolata populations have developed striking differences in their responses to local climates and stratification requirements suggesting that a complex interplay of pre-adaptation, rapid evolutionary changes, and phenotypic plasticity result in locally adapted populations.We document inter-population variation in Alliaria petiolata germination and emergence pattern after 150 years of residence time in North America. Laboratory trials did not predict long-term emergence pattern observed over 13 years in a common garden. Our data suggest that an interplay of pre-adaptation, rapid evolutionary changes and phenotypic plasticity result in locally adapted populations.
      PubDate: 2017-10-20T03:38:16.14569-05:0
      DOI: 10.1111/1365-2745.12854
       
  • Mycorrhizae, invasions, and the temporal dynamics of mutualism disruption
    • Authors: Sara Grove; Karen A. Haubensak, Catherine Gehring, Ingrid M. Parker
      Pages: 1496 - 1508
      Abstract: An increasingly recognized impact of plant invaders is the disruption of positive interactions between native plants and their belowground mutualistic mycorrhizal fungi. We reviewed 112 studies from 61 publications that report invader impacts on mycorrhizal fungi. We describe emerging patterns on the frequency of negative, neutral and positive invader effects on mycorrhizal fungal abundance, richness and community composition, and we evaluate how these outcomes vary with invasion age. We also describe the evidence for three mechanisms of disruption: (1) plant-plant competition that alters host quantity or quality (2) changes in soil properties such as nutrient availability and (3) allelopathy.Invaders can disrupt native mutualisms if they are non-mycorrhizal, associate with a different type of mycorrhiza, or associate with different taxa of the same type of mycorrhiza as the native plants. Invaders that enrich soil nutrients can cause declines in mycorrhizal abundance, shifts in fungal community composition, and cause native plants to reduce their dependence on mycorrhizas. Invaders that produce allelopathic compounds cause mycorrhizal abundance to decrease and alter community composition because of variation in the sensitivity of different fungi to toxins.While the evidence for disruption of the mycorrhizal mutualism with invasion is strong, temporal patterns have not yet emerged from the literature. Invasion age was not clearly associated with extent of disruption, and the timing of recovery following invader removal was highly variable. Differences in the biology of native and invasive plants, their interactions with mycorrhizal fungi and the surrounding landscape contributed to this variation.Synthesis. Our systematic review suggests that invaders frequently decrease mycorrhizal abundance and alter fungal community composition while only occasionally affecting fungal species richness. The development of invader impacts, as well as the restoration of native communities after invader removal, are influenced by a suite of plant, fungal and environmental traits that change over time. However, few studies have examined the temporal dynamics of mycorrhizal disruption, and results are variable. Future research should focus on the temporal scale of mutualism disruption while considering plant phylogenetics and demography, fungal functional traits such as spore longevity and dispersal, and soil chemistry.Our systematic review suggests that invaders frequently decrease mycorrhizal abundance and alter fungal community composition while only occasionally affecting fungal species richness. The development of invader impacts, as well as the restoration of native communities after invader removal, are influenced by a suite of plant, fungal and environmental traits that change over time. However, few studies have examined the temporal dynamics of mycorrhizal disruption, and results are variable. Future research should focus on the temporal scale of mutualism disruption while considering plant phylogenetics and demography, fungal functional traits such as spore longevity and dispersal, and soil chemistry.
      PubDate: 2017-10-20T03:38:12.654622-05:
      DOI: 10.1111/1365-2745.12853
       
  • Invasive Bromus tectorum alters natural selection in arid systems
    • Authors: Elizabeth A. Leger; Erin M. Goergen
      Pages: 1509 - 1520
      Abstract: While much research has documented the impact of invaders on native communities and ecosystem services, there has been less work quantifying how invasion affects the genetic composition of native populations. That is, when invaders dominate a community, can they shift selection regimes and impact the evolutionary trajectory of native populations'The invasion of the annual grass Bromus tectorum in the Intermountain West provides an opportunity to quantify the effects of invasion on natural selection in wild populations. The shift from a perennial-dominated native community to one dominated by a highly competitive annual species alters the timing and intensity of competitive pressure, which has the potential to strongly shift selection regimes for native plants.To quantify traits under selection in contrasting environments, we planted seeds of two native perennial grasses, Elymus multisetus and Poa secunda, into three invaded, invaded but weeded and relatively uninvaded sagebrush systems. We quantified phenotypic traits of seedlings from separate maternal plants, describing differences in phenotypes among individuals. We then asked which traits were associated with survival and plant size in adjacent invaded and uninvaded sagebrush systems, following individual seed performance for 3 years.We found evidence for divergent selection between invaded and uninvaded sagebrush systems, with contrasting phenotypic traits associated with greater survival or plant size in these different growing conditions at all three field sites. For example, at one field site, P. secunda families with higher root tip production were more likely to survive in invaded and weeded environments, but this was not the case in uninvaded environments. Similarly, for E. multisetus, root mass fraction, seed mass and allocation to coarse or fine roots affected survival and plant size, again with contrasting relationships across invaded, weeded or uninvaded environments.Synthesis. Impacts of invasive species extend beyond ecosystem and community composition changes and can affect the evolutionary trajectory of native populations. By quantifying natural selection in invaded landscapes, we identified phenotypic traits that are potentially adaptive in these invaded systems. Importantly, these traits differed from traits associated with success in uninvaded communities. This insight into adaptive, contemporary evolution in native species can guide restoration and conservation efforts.Invasive Bromus tectorum has drastically changed conditions in sagebrush steppe communities in the Intermountain West. Using precision seeding methods and reciprocal transplant studies, we examined changes in natural selection associated with plant invasion. Focusing on seedlings of two native perennial grasses, we found that contrasting phenotypes were associated with survival and plant size in adjacent invaded/uninvaded communities. Our results demonstrate that the impacts of invasive species extend beyond ecosystem and community composition changes, and that invasive species can also affect the evolutionary trajectory of native populations.
      PubDate: 2017-10-20T03:38:22.540003-05:
      DOI: 10.1111/1365-2745.12852
       
  • Alternative pathways to landscape transformation: invasive grasses, burn
           severity and fire frequency in arid ecosystems
    • Authors: Rob Klinger; Matt Brooks
      Pages: 1521 - 1533
      Abstract: Arid ecosystems are often vulnerable to transformation to invasive-dominated states following fire, but data on persistence of these states are sparse. The grass/fire cycle is a feedback process between invasive annual grasses and fire frequency that often leads to the formation of alternative vegetation states dominated by the invasive grasses. However, other components of fire regimes, such as burn severity, also have the potential to produce long-term vegetation transformations. Our goal was to evaluate the influence of both fire frequency and burn severity on the transformation of woody-dominated communities to communities dominated by invasive grasses in major elevation zones of the Mojave Desert of western North America.We used a chronosequence design to collect data on herbaceous and woody cover at 229 unburned reference plots and 578 plots that burned between 1972 and 2010. We stratified the plots by elevation zone (low, mid, high), fire frequency (1–3 times) and years post-fire (YPF; 1–5, 6–10, 11–20 and 21–40 YPF). Burn severity for each plot was estimated by the difference normalized burn ratio.We identified two broad post-fire successional pathways. One was an outcome of fire frequency, resulting in a strong potential transformation via the grass/fire cycle. The second pathway was driven by burn severity, the critical aspect being that long-term transformation of a community could occur from just one fire in areas that burned at high or sometimes moderate severity. Dominance by invasive grasses was most likely to occur in low-and high-elevation communities; cover of native herbaceous species was often greater than that of invasive grasses in the mid-elevation zone.Synthesis. Invasive grasses can dominate a site that burned only one time in many decades at high severity, or a site that burned at low severity but multiple times in the same time period. However, high burn severity may predispose areas to more frequent fire because they have relatively high cover of invasive annual grass, suggesting burn severity and fire frequency have both independent and synergistic effects. Resilience in vegetation structure following fire in many arid communities may be limited to a narrow window of low burn severity in areas that have not burned in many decades.Invasive grasses can dominate a site that burned only one time in many decades at high severity, or a site that burned at low severity but multiple times in the same time period. However, high burn severity may predispose areas to more frequent fire because they have relatively high cover of invasive annual grass, suggesting burn severity and fire frequency have both independent and synergistic effects. Resilience in vegetation structure following fire in many arid communities may be limited to a narrow window of low burn severity in areas that have not burned in many decades.
      PubDate: 2017-10-20T03:38:22.003657-05:
      DOI: 10.1111/1365-2745.12863
       
  • Hemispheric asymmetries in herbivory: do they exist'
    • Authors: Mikhail V. Kozlov; Tero Klemola
      Pages: 1571 - 1574
      Abstract: Latitudinal patterns in herbivory are widely debated. A recent publication (Zhang et al., Journal of Ecology, 104, 2016: 1089–1095) concluded that the absolute levels of herbivory (hypothesis 1), as well as latitudinal and climatic gradients in herbivory (hypothesis 2), differ between the hemispheres.Zhang et al. (2016), among others, used a measure of plant damage from Moles & Westoby (Oikos, 90, 2000: 517–524) that greatly overestimates insect herbivory, and they did not include the main effect of hemisphere in their linear model that explored the relationship between herbivory and latitude. After correction of the values extracted from Moles & Westoby (2000), none of several statistical models that tested both hypotheses simultaneously (i.e. including hemisphere, latitude/climate and their interaction) confirmed the existence of statistically significant differences in the patterns of insect herbivory between the hemispheres.Synthesis. The current level of knowledge does not provide grounds to conclude that hemispheric asymmetries exist either in the average levels of insect herbivory or in the relationships between herbivory and latitude or climate.Predicted percentages (with 95% confidence intervals from generalized linear mixed model) of insect herbivory in relation to the latitude in the Northern and Southern Hemispheres demonstrate the absence of hemispheric asymmetries both in the average level of insect herbivory and in the relationship between herbivory and latitude.
      PubDate: 2017-09-20T10:50:21.347502-05:
      DOI: 10.1111/1365-2745.12825
       
  • A re-evaluation of hemispheric asymmetries in herbivory: a response to
           Kozlov & Klemola 2017
    • Authors: Shuang Zhang; Yuxin Zhang, Keming Ma
      Pages: 1575 - 1579
      Abstract: Kozlov & Klemola (Journal of Ecology, 105, 2017: 000-000) argued that our conclusion about hemispheric asymmetries in herbivory is not supported after the replacement of data points extracted from Moles & Westoby (Oikos, 90, 2000: 517–524.).To re-evaluate the asymmetries in herbivory, we analysed the revised dataset according to Kozlov & Klemola's (2017) suggestion, as well as the dataset used in Kozlov et al. (Global Ecology and Biogeography, 24, 2015: 1126–1135.).All the analyses showed that herbivory decreased with latitude only in the Northern hemisphere, but in the Southern hemisphere, herbivory showed no relation to latitude. Model selection showed that in both datasets, hemisphere is a key determinant of herbivory, with Southern hemisphere having higher levels of herbivory than the Northern hemisphere.Synthesis. Based on currently available data collected from publications, we found evidence for hemispheric asymmetries in herbivory. This conclusion is unlikely to change even when the controversial data points are replaced.Based on currently available data collected from publications, we found evidence for hemispheric asymmetries in herbivory. This conclusion is unlikely to change even when the controversial data points are replaced.
      PubDate: 2017-09-20T07:26:45.139522-05:
      DOI: 10.1111/1365-2745.12828
       
  • Dissecting the contributions of dispersal and host properties to the local
           abundance of a tropical mistletoe
    • Authors: Marcos A. Caraballo-Ortiz; Aarón González-Castro, Suann Yang, Claude W. dePamphilis, Tomás A. Carlo
      Pages: 1657 - 1667
      Abstract: The interplay between dispersal and adaptation to local environments ultimately determines the distribution of plant species, but their relative contribution remains little understood. Tropical mistletoes provide the opportunity to dissect these contributions of dispersal and adaptation, because as hemiparasitic plants, they are typically adapted to grow on a handful of species within diverse tropical communities and are non-randomly dispersed by mutualistic frugivorous birds.Here we hypothesized that the primary determinant of the abundance of a tropical mistletoe (Dendropemon caribaeus, Loranthaceae) in Puerto Rico will be the compatibility between the mistletoe and plant species in a community. Alternatively, the mistletoe's abundance could be primarily shaped by other factors such as the availability of potential host plants, or factors that determine how mistletoe seeds are dispersed by avian frugivores. We conducted surveys and experiments to assess the capacity of this mistletoe to grow on trees available in the local community, and measured the monthly phenology and seed dispersal patterns of the mistletoe and other bird-dispersed plants in the community over a period of 4 years. A path model was used to evaluate how the abundance of the mistletoe was shaped by host abundance, fruiting phenology, bird dispersal and compatibilities with host plants.Our analyses show that the compatibility between mistletoe and host tree species, measured by mistletoe survival and growth rate, was the most important factor for mistletoe abundance. The next most important factor was the phenological characteristics of the hosts; this outcome likely arose because frugivory and seed dispersal services for mistletoes and hosts are performed by the same birds.Synthesis. Mistletoes often parasitize only a subset of the suitable plant species that are available in a given community. Our results indicate that such patterns are not only determined by host quality and abundance but also by the phenological patterns of trees that influence the probabilities of mistletoe seeds being deposited on them by shared avian seed dispersers.Mistletoes often parasitize only a subset of the suitable plant species that are available in a given community. Our results indicate that such patterns are not only determined by host quality and abundance, but also by the phenological patterns of trees that influence the probabilities of mistletoe seeds being deposited on them by shared avian seed dispersers.
      PubDate: 2017-05-22T19:00:01.840007-05:
      DOI: 10.1111/1365-2745.12795
       
  • Biological Flora of the British Isles: Sorbus torminalis
    • Authors: Peter A. Thomas
      Pages: 1806 - 1831
      Abstract: This account presents information on all aspects of the biology of Sorbus torminalis (L.) Crantz (Wild Service-tree) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation.Sorbus torminalis is an uncommon, mostly small tree (but can reach 33 m) native to lowland England and Wales, and temperate and Mediterranean regions of mainland Europe. It is the most shade-tolerant member of the genus in the British Isles, and as a result, it is more closely associated with woodland than any other British species. Like other British Sorbus species, however, it grows best where competition for space and sunlight is limited. Seedlings are shade tolerant but adults are only moderately so. This, combined with its low competitive ability, restricts the best growth to open areas. In shade, saplings and young adults form a sapling bank, showing reproduction and extensive growth only when released. Sorbus torminalis tolerates a wide range of soil reaction (pH 3·5–8·0) but grows best on calcareous clays and thin soils over limestone.Sorbus torminalis is a sexual, diploid, non-apomictic species that has hybridised with a number of other Sorbus species to form microspecies. The hermaphrodite flowers are primarily insect pollinated. Seed production is reliable only in warm years, especially at the edge of its range, although even then seed viability is low. The fruits are primarily dispersed by carnivorous mammals. Seeds display embryo dormancy but most will germinate the first spring after falling.This tree is very tolerant of short droughts but only moderately tolerant of frost, hence its southerly and lowland distribution. It faces no particular individual threats although the small size of most populations makes it susceptible to habitat loss and fragmentation, particularly through the loss of open coppiced areas. As a consequence, it appears to be declining throughout Britain and Europe despite its wide range of historical uses and the high value of its timber. The extent to which these losses will be offset by increases due to climate change is unknown.Sorbus torminalis is an uncommon tree of lowland woodlands across Europe, once voted the world's most beautiful timber. Although tolerant of a wide range of soils and light, it grows best in open woodlands on clays or limestone. It is in decline throughout Europe partially due to the loss of coppicing, leading to denser woodlands.
      PubDate: 2017-10-11T03:21:33.064284-05:
      DOI: 10.1111/1365-2745.12857
       
  • Corrigendum
    • Pages: 1832 - 1832
      PubDate: 2017-09-11T10:25:43.751305-05:
      DOI: 10.1111/1365-2745.12856
       
  • Corrigendum
    • Pages: 1833 - 1833
      PubDate: 2017-09-25T10:32:15.746997-05:
      DOI: 10.1111/1365-2745.12867
       
 
 
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