for Journals by Title or ISSN
for Articles by Keywords
help
  Subjects -> BIOLOGY (Total: 2601 journals)
    - BIOCHEMISTRY (192 journals)
    - BIOENGINEERING (63 journals)
    - BIOLOGY (1322 journals)
    - BIOPHYSICS (42 journals)
    - BIOTECHNOLOGY (145 journals)
    - BOTANY (195 journals)
    - CYTOLOGY AND HISTOLOGY (24 journals)
    - ENTOMOLOGY (54 journals)
    - GENETICS (136 journals)
    - MICROBIOLOGY (210 journals)
    - MICROSCOPY (9 journals)
    - ORNITHOLOGY (23 journals)
    - PHYSIOLOGY (66 journals)
    - ZOOLOGY (120 journals)

ZOOLOGY (120 journals)                  1 2     

Acta Herpetologica     Open Access   (Followers: 4)
Acta Theriologica     Full-text available via subscription   (Followers: 6)
Acta Zoologica     Hybrid Journal   (Followers: 3)
Acta zoológica mexicana     Open Access  
African Invertebrates     Open Access  
African Journal of Herpetology     Full-text available via subscription   (Followers: 1)
African Zoology     Open Access   (Followers: 6)
animal     Hybrid Journal   (Followers: 3)
Animal Behaviour     Hybrid Journal   (Followers: 197)
Animal Biology     Hybrid Journal   (Followers: 8)
Animal Biology & Animal Husbandry     Open Access   (Followers: 5)
Animal Biotelemetry     Open Access   (Followers: 2)
Animal Genetics     Hybrid Journal   (Followers: 7)
Animal Migration     Open Access   (Followers: 1)
Animal Studies Journal     Open Access   (Followers: 4)
Annales UMCS, Zootechnica     Open Access   (Followers: 1)
Annales Zoologici     Full-text available via subscription  
Annales Zoologici Fennici     Open Access  
Annals of Animal Science     Open Access   (Followers: 2)
Annual Review of Animal Biosciences     Full-text available via subscription   (Followers: 4)
Anthropozoologica     Full-text available via subscription   (Followers: 4)
Anthrozoos : A Multidisciplinary Journal of The Interactions of People & Animals     Full-text available via subscription   (Followers: 5)
Applied Animal Behaviour Science     Hybrid Journal   (Followers: 11)
Applied Entomology and Zoology     Partially Free   (Followers: 3)
Aquatic Mammals     Full-text available via subscription   (Followers: 4)
Aquatic Sciences     Hybrid Journal   (Followers: 11)
Asian Journal of Animal and Veterinary Advances     Open Access   (Followers: 5)
Australian Journal of Zoology     Hybrid Journal   (Followers: 1)
Bioacoustics : The International Journal of Animal Sound and its Recording     Partially Free   (Followers: 2)
Bird Conservation International     Hybrid Journal   (Followers: 13)
Bird Study     Full-text available via subscription   (Followers: 11)
Brazilian Journal of Veterinary Research and Animal Science     Open Access   (Followers: 6)
British Birds     Full-text available via subscription   (Followers: 8)
Bulletin of the Museum of Comparative Zoology     Full-text available via subscription   (Followers: 3)
Canadian Journal of Animal Science     Full-text available via subscription   (Followers: 4)
Canadian Journal of Zoology     Full-text available via subscription   (Followers: 11)
Contributions to Zoology     Open Access   (Followers: 3)
Der Zoologische Garten     Full-text available via subscription   (Followers: 2)
Ecology of Freshwater Fish     Hybrid Journal   (Followers: 14)
Edentata     Open Access  
European Journal of Taxonomy     Open Access   (Followers: 2)
Euscorpius     Open Access  
EvoDevo     Open Access   (Followers: 1)
Fieldiana Zoology     Full-text available via subscription   (Followers: 2)
Fish and Fisheries     Hybrid Journal   (Followers: 26)
Frontiers in Zoology     Open Access   (Followers: 6)
Graellsia     Open Access  
Hystrix, the Italian Journal of Mammalogy     Open Access  
i-Perception     Open Access   (Followers: 3)
Iheringia. Série Zoologia     Open Access  
In Vitro Cellular & Developmental Biology - Animal     Hybrid Journal   (Followers: 1)
Integrative Zoology     Hybrid Journal  
International Journal of Odonatology     Hybrid Journal   (Followers: 1)
International Journal of Zoological Research     Open Access   (Followers: 2)
International Journal of Zoology     Open Access   (Followers: 2)
International Zoo Yearbook     Hybrid Journal   (Followers: 1)
Invertebrate Reproduction & Development     Hybrid Journal   (Followers: 2)
ISRN Zoology     Open Access  
Italian Journal of Animal Science     Open Access   (Followers: 2)
Italian Journal of Zoology     Hybrid Journal   (Followers: 2)
Journal of Agrobiology     Open Access   (Followers: 2)
Journal of Animal Ecology     Hybrid Journal   (Followers: 26)
Journal of Animal Physiology and Animal Nutrition     Hybrid Journal   (Followers: 5)
Journal of Apicultural Science     Open Access  
Journal of Applied Animal Research     Hybrid Journal  
Journal of Basic & Applied Zoology : Physiology     Open Access  
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology     Hybrid Journal   (Followers: 2)
Journal of Experimental Zoology Part B : Molecular and Developmental Evolution     Hybrid Journal  
Journal of Freshwater Ecology     Hybrid Journal   (Followers: 9)
Journal of Insects     Open Access  
Journal of Venomous Animals and Toxins     Open Access   (Followers: 3)
Journal of Venomous Animals and Toxins including Tropical Diseases     Open Access  
Journal of Wildlife Management     Hybrid Journal   (Followers: 22)
Journal of Zoo and Aquarium Research     Open Access  
Journal of Zoological Systematics and Evolutionary Research     Hybrid Journal   (Followers: 5)
Journal of Zoology     Hybrid Journal   (Followers: 9)
Laboratory Animals     Hybrid Journal   (Followers: 11)
Mammalia     Full-text available via subscription   (Followers: 7)
Marine Ecology Progress Series MEPS     Full-text available via subscription   (Followers: 8)
Mastozoología Neotropical     Open Access  
Memorias de la Conferencia Interna en Medicina y Aprovechamiento de Fauna Silvestre, Exótica y no Convencional     Open Access  
Neotropical Primates     Open Access  
New Zealand Journal of Zoology     Hybrid Journal  
Papéis Avulsos de Zoologia     Open Access   (Followers: 1)
Parasite     Open Access   (Followers: 5)
Physiological and Biochemical Zoology     Full-text available via subscription   (Followers: 5)
Polish Journal of Entomology     Open Access   (Followers: 2)
Protist Genomics     Open Access  
Research in Zoology     Open Access   (Followers: 1)
Revista Brasileira de Zoologia     Open Access  
Revista de Biología Marina y Oceanografía     Open Access   (Followers: 1)
Revista de Zoologia     Open Access   (Followers: 1)
Revista del Museo Argentino de Ciencias Naturales     Open Access  
Russian Journal of Herpetology     Full-text available via subscription   (Followers: 1)
Scientific Journal of Animal Science     Open Access   (Followers: 3)
Scientific Journal of Zoology     Open Access   (Followers: 2)
SHILAP Revista de Lepidopterologia     Open Access   (Followers: 2)
Skeletal Muscle     Open Access   (Followers: 1)
Sri Lanka Journal of Aquatic Sciences     Open Access  
Travaux du Muséum National d’Histoire Naturelle “Grigore Antipa”     Open Access  

        1 2     

Journal Cover Journal of Animal Ecology
   [28 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 0021-8790 - ISSN (Online) 1365-2656
     Published by John Wiley and Sons Homepage  [1603 journals]   [SJR: 2.606]   [H-I: 94]
  • Life-history trade-offs mediate ‘personality’ variation in two
           colour morphs of the pea aphid, Acyrthosiphon pisum
    • Authors: W. Schuett; S.R.X. Dall, M.H. Kloesener, J. Baeumer, F. Beinlich, T. Eggers
      Pages: n/a - n/a
      Abstract: (1) Life-history trade-offs are considered a major driving force in the emergence of consistent behavioural differences (personality variation); but empirical tests are scarce. (2) We investigated links between a personality trait (escape response), life-history and state variables (growth rate, size and age at first reproduction, age-dependent reproductive rates, lifetime reproductive success, lifespan) in red and green colour morphs of clonal pea aphids, Acyrthosiphon pisum. Escape response (dropping/non-dropping off a plant upon a predatory attack) was measured repeatedly to classify individuals as consistent droppers, consistent non-droppers or inconsistents. (3) Red morphs experienced stronger trade-offs between early reproduction and lifespan than green morphs; and red consistent (non-)droppers had highest lifetime reproductive success. Red droppers followed a risk-averse life-history strategy (high late reproduction), red non-droppers a risk-prone strategy (high early reproduction), while reproductive rates were equivalent for all green behavioural types and red inconsistents. (4) This suggests that red morphs suffer the highest costs of dropping (they are most conspicuous to predators), which ‘equivalates’ fitness payoffs to both risk-takers (red non-droppers) and risk-averse red droppers. The strong trade-off also means that committing to a particular lifestyle (being consistent) maximises fitness. (5) Our study suggests that life-history trade-offs likely mediate personality variation but effects might depend on interactions with other organismal characteristics (here: colour morph). This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-18T22:47:26.75794-05:0
      DOI: 10.1111/1365-2656.12263
       
  • Species undersampling in tropical bat surveys: effects on emerging
           biodiversity patterns
    • Authors: Christoph F. J. Meyer; Ludmilla M. S. Aguiar, Luis F. Aguirre, Julio Baumgarten, Frank M. Clarke, Jean-François Cosson, Sergio Estrada Villegas, Jakob Fahr, Deborah Faria, Neil Furey, Mickaël Henry, Richard K. B. Jenkins, Thomas H. Kunz, M. Cristina MacSwiney Gonzalez, Isabel Moya, Jean-Marc Pons, Paul A. Racey, Katja Rex, Erica M. Sampaio, Kathryn E. Stoner, Christian C. Voigt, Dietrich Staden, Christa D. Weise, Elisabeth K. V. Kalko
      Pages: n/a - n/a
      Abstract: 1. Undersampling is commonplace in biodiversity surveys of species-rich tropical assemblages in which rare taxa abound, with possible repercussions for our ability to implement surveys and monitoring programs in a cost-effective way. 2. We investigated the consequences of information loss due to species undersampling (missing subsets of species from the full species pool) in tropical bat surveys for the emerging patterns of species richness and compositional variation across sites. 3. For 27 bat assemblage datasets from across the tropics, we used correlations between original datasets and subsets with different numbers of species deleted either at random, or according to their rarity in the assemblage, to assess to what extent patterns in species richness and composition in data subsets are congruent with those in the initial dataset. We then examined to what degree high sample representativeness (r ≥ 0.8) was influenced by biogeographic region, sampling method, sampling effort, or structural assemblage characteristics. 4. For species richness, correlations between random subsets and original datasets were strong (r ≥ 0.8) with moderate (ca. 20%) species loss. Bias associated with information loss was greater for species composition; on average ca. 90% of species in random subsets had to be retained to adequately capture among-site variation. For non-random subsets, removing only the rarest species (on average ~10% of the full dataset) yielded strong correlations (r> 0.95) for both species richness and composition. Eliminating greater proportions of rare species resulted in weaker correlations and large variation in the magnitude of observed correlations among datasets. 5. Species subsets that comprised ca. 85% of the original set can be considered reliable surrogates, capable of adequately revealing patterns of species richness and temporal or spatial turnover in many tropical bat assemblages. Our analyses thus demonstrate the potential as well as limitations for reducing survey effort and streamlining sampling protocols, and consequently for increasing the cost-effectiveness in tropical bat surveys or monitoring programs. The dependence of the performance of species subsets on structural assemblage characteristics (total assemblage abundance, proportion of rare species), however, underscores the importance of adaptive monitoring schemes and of establishing surrogate performance on a site-by-site basis based on pilot surveys. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-18T22:47:25.025463-05:
      DOI: 10.1111/1365-2656.12261
       
  • Climate and the landscape of fear in an African savanna
    • Authors: Corinna Riginos
      Pages: n/a - n/a
      Abstract: 1.Herbivores frequently have to make tradeoffs between two basic needs: the need to acquire forage and the need to avoid predation. One manifestation of this tradeoff is the “landscape of fear” phenomenon – wherein herbivores avoid areas of high perceived predation risk even if forage is abundant or of high quality in those areas. Although this phenomenon is well-established among invertebrates, its applicability to terrestrial large herbivores remains debated, in part because experimental evidence is scarce. 2.This study was designed to (a) experimentally test the effects of tree density – a key landscape feature associated with predation risk for African ungulates – on herbivore habitat use, and (b) establish whether habitat use patterns could be explained by tradeoffs between foraging opportunities and predation risk-avoidance. 3.In a Kenyan savanna system, replicate plots dominated by the tree Acacia drepanolobium were cleared, thinned, or left intact. Ungulate responses were measured over four years, which included years of moderate rainfall as well as a severe drought. 4.Under average rainfall conditions, most herbivores (primarily plains zebra, Grant's gazelle, and hartebeest) favored sites with fewer trees and higher visibility – regardless of grass production – while elephants (too large to be vulnerable to predation) favored sites with many trees. During the drought, however, herbivores favored sites that had high grass biomass, but not high visibility. Thus, during the drought, herbivores sought areas where food was more abundant, despite probable higher risk of predation. 5.These results illustrate that the “landscape of fear”, and the associated interactions between top-down and bottom-up effects, is not static, but rather shifts markedly under different conditions. Climate thus has the potential to alter the strength and spatial dynamics of behaviorally-mediated cascades in large herbivore systems. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-18T10:48:00.244796-05:
      DOI: 10.1111/1365-2656.12262
       
  • Relationship between growth and standard metabolic rate: measurement
           artefacts and implications for habitat use and life-history adaptation in
           salmonids
    • Authors: Jordan Rosenfeld; Travis Leeuwen, Jeffrey Richards, David Allen
      Pages: n/a - n/a
      Abstract: 1) Mass-specific standard metabolic rate (SMR, or maintenance metabolism) varies greatly among individuals. Metabolism is particularly sensitive to variation in food consumption and growth creating the potential for significant bias in measured SMR for animals that are growing (e.g. juveniles) or of uncertain nutritional status. 2) Consequently, interpreting individual variation in metabolism requires a sound understanding of the potentially confounding role of growth, and the relative importance of fixed (genetic) vs. environmental drivers of SMR variation. 3) We review the role of growth in measured SMR variation in juvenile salmonids, with the goals of i) understanding the contribution of growth (and food consumption) to SMR variation through ontogeny, ii) understanding the relative contributions of tissue maintenance and biosynthesis (overhead costs of growth) to apparent SMR variation, and iii) using intrinsic growth effects on SMR to model how alternate life-history strategies may influence growth and measured SMR in juvenile salmonids. 3) SMR measures on juveniles, even when post-absorptive, may be inflated by delayed growth-associated overhead costs unless juveniles are on a maintenance ration (i.e. not growing). Empirical measurements of apparent SMR in food restricted vs. satiated 2 to 5 g juvenile salmon demonstrate that estimates may be inflated by as much as 67% due to delayed overhead costs of growth, even when SMR measurements are made 35 hours post-feeding. 4) These results indicate that a substantial component of variation in apparent SMR among juvenile salmonids may be associated with i) environmentally-driven variation in ration (where elevated SMR measurements are an artefact of delayed growth overhead costs), ii) intrinsic (genetic) or plastic organ system tradeoffs related to increasing investment in metabolically expensive digestive tissue responsible for processing food, and iii) intrinsic (genetic) variation in maximum body size and growth among individuals or life-history types. We suggest that selection for differences in adult body size among resident and anadromous forms leading to differences in juvenile growth trajectories may contribute to both SMR variation and habitat segregation in freshwater, where juveniles with higher growth are constrained to foraging in high velocity habitats to meet their greater consumption needs. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-16T02:30:46.877771-05:
      DOI: 10.1111/1365-2656.12260
       
  • Fitness prospects: effects of age, sex and recruitment age on reproductive
           value in a long-lived seabird
    • Authors: He Zhang; Maren Rebke, Peter H. Becker, Sandra Bouwhuis
      Pages: n/a - n/a
      Abstract: (1) Reproductive value is an integrated measure of survival and reproduction fundamental to understanding life-history evolution and population dynamics, but little is known about intra-specific variation in reproductive value and factors explaining such variation, if any. (2) By applying generalized additive mixed models to longitudinal individual-based data of the common tern Sterna hirundo we estimated age-specific annual survival probability, breeding probability and reproductive performance, based on which we calculated age-specific reproductive values. We investigated effects of sex and recruitment age on each trait. (3) We found age effects on all traits, with survival and breeding probability declining with age, while reproductive performance first improved with age before levelling off. We only found a very small, marginally significant, sex-effect on survival probability, but evidence for decreasing age-specific breeding probability and reproductive performance with recruitment age. (4) As a result, males had slightly lower age-specific reproductive values than females, while birds of both sexes that recruited at the earliest ages of 2 and 3 years (i.e. 54% of the tern population) had somewhat higher fitness prospects than birds recruiting at later ages. While the recruitment age effects on breeding probability and reproductive performance were statistically significant, these effects were not large enough to translate to significant effects on reproductive value. (5) Age-specific reproductive values provided evidence for senescence, which came with fitness costs in a range of 17-21% for the sex-recruitment age groups. (6) Our study suggests that intra-specific variation in reproductive value may exist, but that, in the common tern, the differences are small. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-16T02:30:01.074599-05:
      DOI: 10.1111/1365-2656.12259
       
  • A continental scale trophic cascade from wolves through coyotes to foxes
    • Authors: Thomas M Newsome; William J Ripple
      Pages: n/a - n/a
      Abstract: Top-down processes, via the direct and indirect effects of interspecific competitive killing (no consumption of the kill) or intraguild predation (consumption of the kill), can potentially influence the spatial distribution of terrestrial predators, but few studies have demonstrated the phenomenon at a continental scale. For example, in North America, grey wolves (Canis lupus) are known to kill coyotes (Canis latrans), and coyotes, in turn, may kill foxes (Vulpes spp.), but the spatial effects of these competitive interactions at large scales are unknown. Here, we analyse fur return data across eight jurisdictions in North America to test whether the presence or absence of wolves has caused a continent-wide shift in coyote and red fox (Vulpes vulpes) density. Our results support the existence of a continental scale cascade whereby coyotes outnumber red foxes in areas where wolves have been extirpated by humans, whereas red foxes outnumber coyotes in areas where wolves are present. However, for a distance of up to 200 km on the edge of wolf distribution, there is a transition zone where the effects of top-down control are weakened, possibly due to the rapid dispersal and reinvasion capabilities of coyotes into areas where wolves are sporadically distributed or at low densities. Our results have implications for understanding how the restoration of wolf populations across North America could potentially affect co-occurring predators and prey. We conclude that large carnivores may need to occupy large continuous areas to facilitate among-carnivore cascades and that studies of small areas may not be indicative of the effects of top-down mesopredator control. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-14T10:05:25.254605-05:
      DOI: 10.1111/1365-2656.12258
       
  • Ecological generalism and behavioral innovation in birds: technical
           intelligence or the simple incorporation of new foods'
    • Authors: S Ducatez; J Clavel, L Lefebvre
      Abstract: 1.Generalist species are more successful than specialists in anthropogenically‐modified environments or in environments in which they have been introduced, but the nature of the link between generalism and establishment success is unclear. 2.A higher feeding innovation rate has previously been reported in habitat generalist birds from North America. By allowing them to exploit new resources, this higher feeding innovation rate might explain the generalists’ advantage. This result might be due to generalists being more likely to find new resources because they are exposed to more diverse environmental conditions. Alternatively, they might differ from specialists in other traits, in particular cognitive skills that might allow them to innovate more complex food searching and handling techniques. 3.To test these hypotheses, we separated avian feeding innovations into a “technical” (novel searching and handling behavior) and a “food type” (incorporation of a new food in a species’ diet) category. Technical innovations, but not food type innovations, have previously been shown to correlate with avian brain size, suggesting they reflect cognitive ability. We used a worldwide database of 2339 feeding innovations recorded in the literature, covering a total of 765 avian species and assessed the correlations between brain size and feeding innovation rates on one side and habitat and diet generalism on the other. 4.Habitat generalism was positively related with food type innovation rate, but not technical innovation rate or brain size. This suggests that habitat generalist species are more likely to incorporate new food types in their diet because of higher chances to find new food resources in their environment, or of a higher opportunism, but not enhanced cognitive skills. In contrast, diet generalist species had higher food type and technical innovation rates, as well as larger brains, suggesting that cognitive skills might help species expand their diet breadth, or that an increase in diet breadth might favor the evolution of enhanced cognitive abilities. 5.Our results provide new insights into the nature of the generalists’ advantage in the face of environmental changes, and suggest that dietary and habitat generalism are different, but convergent, routes to feeding flexibility and adaptation to changed environments. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-06T10:17:27.327537-05:
      DOI: 10.1111/1365-2656.12255
       
  • Allometric scaling of indirect effects: Body size ratios predict
           non‐consumptive effects in multi‐predator systems
    • Authors: Lauren Krenek; Volker H.W. Rudolf
      Abstract: 1Non‐consumptive effects (NCES) frequently lead to non‐independent effects of multiple predators. While such emergent predator effects are ubiquitous in natural communities, the strength of these effects varies among studies and systems, making it difficult to predict a priory how changes in predator diversity influence prey suppression. Thus, identifying general scaling rules which can explain this variation of non‐independent effects is vital for modeling natural communities and how they respond to biodiversity loss. 2Body size is a key trait determining the nature and strength of ecological interactions. While great progress has been made using allometric relationships to predict the interaction strength of predator‐prey pairs, it is unknown whether similar relationships explain variation in the strength of NCEs, and how they are related to consumptive effects. 3Here we experimentally manipulate the relative size difference of multiple predators to determine whether NCEs follow general allometric scaling relationships in an aquatic multi‐predator system. 4Results demonstrate that the presence and strength of NCEs can vary dramatically across predator combinations. However, this variation scaled predictably with the size ratio of predators; increasing the size difference among predators increased NCEs. This pattern was driven by a size‐mediated shift in “food web motif” from competition to intraguild predation and a positive correlation of NCEs and intraguild predation rate. 5Results indicate that models which assume that consumers have independent effects are particularly likely to make erroneous predictions when predators differ substantially in size, but simple allometric relationships of NCEs could be used to correct this bias. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-06T10:17:26.11756-05:0
      DOI: 10.1111/1365-2656.12254
       
  • Overcompensation and phase effects in a cyclic common vole population:
           between first and second‐order cycles
    • Authors: Frédéric Barraquand; Adrien Pinot, Nigel G. Yoccoz, Vincent Bretagnolle
      Abstract: Population cycles in voles are often thought to be generated by one‐year delayed density‐dependence on the annual population growth rate. In common voles, however, it has been suggested by Turchin (2003) that some populations exhibit first‐order cycles, resulting from strong overcompensation (i.e. carrying capacity overshoots in peak years, with only an effect of the current year abundance on annual growth rates). We focus on a common vole (Microtus arvalis) population from western France, that exhibits 3‐year cycles. Several overcompensating nonlinear models for populations dynamics are fitted to the data, notably those of Hassell, and Maynard‐Smith and Slatkin. Overcompensating direct density‐dependence (DD) provides a satisfactory description of winter crashes, and one‐year delayed density‐dependence is not responsible for the crashes, thus these are not classical second‐order cycles. A phase‐driven modulation of direct density‐dependence maintains a low‐phase, explaining why the cycles last three years instead of two. Our analyses suggest that some of this phase‐dependence can be expressed as one‐year delayed DD, but phase‐dependence provides a better description. Hence modelling suggests that cycles in this population are first‐order cycles with a low phase after peaks, rather than fully second‐order cycles. However, based on the popular log‐linear second‐order autoregressive model, we would conclude only that negative delayed density‐dependence exists. The additive structure of this model cannot show when delayed DD occurs (here, during lows rather than peaks). Our analyses thus call into question the automated use of second‐order log‐linear models, and suggests that more attention should be given to non‐(log)linear models when studying cyclic populations. From a biological viewpoint, the fast crashes through overcompensation that we found suggest they might be caused by parasites or food rather than predators, though predators might have a role in maintaining the low phase and spatial synchrony. This article is protected by copyright. All rights reserved.
      PubDate: 2014-06-06T08:37:48.597212-05:
      DOI: 10.1111/1365-2656.12257
       
  • Trait‐based diet selection: Prey behaviour and morphology predict
           vulnerability to predation in reef fish communities
    • Authors: Stephanie J. Green; Isabelle M. Côté
      Abstract: 1.Understanding how predators select their prey can provide important insights into community structure and dynamics. However, the suite of prey species available to a predator is often spatially and temporally variable. As a result, species‐specific selectivity data are of limited use for predicting novel predator‐prey interactions because they are assemblage‐specific. 2.We present a method for predicting diet selection that is applicable across prey assemblages, based on identifying general morphological and behavioural traits of prey that confer vulnerability to predation independent of species identity. We apply this trait‐based approach to examining prey selection by Indo‐Pacific lionfish (Pterois volitans), an invasive predator that preys upon species‐rich reef fish communities and is rapidly spreading across the Western Atlantic. 3.We first generate hypotheses about morphological and behavioural traits recurring across fish species that could facilitate or deter predation by lionfish. Constructing generalised linear mixed‐models that account for relatedness among prey taxa, we test whether these traits predict patterns of diet selection by lionfish within two independent data sets collected at different spatial scales: 1) in situ visual observations of prey consumption and availability for individual lionfish, and (2) comparisons of prey abundance in lionfish stomach contents to availability in invaded reefs at large. 4.Both analyses reveal that a number of traits predicted to affect vulnerability to predation, including body size, body shape, position in the water column and aggregation behaviour, are important determinants of diet selection by lionfish. Small, shallow‐bodied solitary fishes found resting on or just above reefs are the most vulnerable. Fishes that exhibit parasite cleaning behaviour experience a significantly lower risk of predation than non‐cleaning fishes, and fishes that are nocturnally active are at significantly greater risk. Together, vulnerable traits heighten the risk of predation by a factor of nearly 200. 5.Our study reveals that a trait‐based approach to studying diet selection yields insights into predator‐prey interactions that are robust across prey assemblages. Importantly, in situ observations of selection yield similar results to broad‐scale comparisons of prey use and availability, which are more typically gathered for predator species. A trait‐based approach could therefore be of use across predator species and ecosystems to predict the outcomes of changing predator‐prey interactions on community dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2014-05-24T10:36:29.250758-05:
      DOI: 10.1111/1365-2656.12250
       
  • Extracting order from elegant chaos: implications of the marine diversity
           spectrum
    • Authors: Thomas J. Webb
      Pages: 741 - 743
      Abstract: Slopes of the diversity spectrum for all of the world's coastal large marine ecosystems for which sufficient data exist. From this, it is possible both to relate the diversity spectrum to environmental parameters (e.g. temperature) and to make regional predictions of unmeasured quantities, such as the diversity of small-bodied species. In Focus: Reuman, D.C., Gislason, H, Barnes, C., Mélin, F. & Jennings, S. (2014) The marine diversity spectrum. Journal of Animal Ecology, 83, 963–979. How do we begin to extract order from the elegant chaos of natural ecosystems' In a landmark new paper published in this issue, Reuman et al. () go back to first principles, combining a range of established body size- and species-centred ecological theories with empirically well-supported relationships to construct a model that enables them to predict key features using only remarkably simple biological and environmental measurements. They test this model using widely available data on the communities living in all of the world's coastal seas. Here, I discuss the key features of their model, and especially how the general patterns they document can lead to further, empirically driven tests of theory across multiple ecosystems. This article discusses a landmark paper published in this issue by Reuman et al. (2014) in which the authors construct a mechanistic model of how diversity varies with body mass in marine ecosystems and test it using widely-available data on the communities living in all of the world's coastal seas.
      PubDate: 2014-06-16T06:47:27.642117-05:
      DOI: 10.1111/1365-2656.12242
       
  • Heat and immunity: an experimental heat wave alters immune functions in
           three-spined sticklebacks ( Gasterosteus aculeatus)
    • Authors: Janine Dittmar; Hannah Janssen, Andra Kuske, Joachim Kurtz, Jörn P. Scharsack
      Pages: 744 - 757
      Abstract: Global climate change is predicted to lead to increased temperatures and more extreme climatic events. This may influence host–parasite interactions, immunity and therefore the impact of infectious diseases on ecosystems. However, little is known about the effects of rising temperatures on immune defence, in particular in ectothermic animals, where the immune system is directly exposed to external temperature change. Fish are ideal models for studying the effect of temperature on immunity, because they are poikilothermic, but possess a complete vertebrate immune system with both innate and adaptive immunity. We used three-spined sticklebacks ( Gasterosteus aculeatus) originating from a stream and a pond, whereby the latter supposedly were adapted to higher temperature variation. We studied the effect of increasing and decreasing temperatures and a simulated heat wave with subsequent recovery on body condition and immune parameters. We hypothesized that the immune system might be less active at low temperatures, but will be even more suppressed at temperatures towards the upper tolerable temperature range. Contrary to our expectation, we found innate and adaptive immune activity to be highest at a temperature as low as 13 °C. Exposure to a simulated heat wave induced long-lasting immune disorders, in particular in a stickleback population that might be less adapted to temperature variation in its natural environment. The results show that the activity of the immune system of an ectothermic animal species is temperature dependent and suggest that heat waves associated with global warming may immunocompromise host species, thereby potentially facilitating the spread of infectious diseases. Heat waves become more frequent events during climate change and may influence host–parasite interactions. Here, we show that the activity of the immune system of an ectothermic animal species is temperature-dependent and suggest that heat waves may immunocompromise host species, thereby potentially facilitating the spread of infectious diseases.
      PubDate: 2014-01-07T13:46:39.486219-05:
      DOI: 10.1111/1365-2656.12175
       
  • Body size-mediated starvation resistance in an insect predator
    • Authors: André Gergs; Tjalling Jager
      Pages: 758 - 768
      Abstract: Individual organisms have to endure transient periods of low-food supply with consequences for growth, reproduction and survival. To resist starvation, animals usually store resources in their bodies: the larger the animals are, the more resources they can carry, but the more energy they need to allocate for maintaining bodily functions. It is unclear how survival relates to body size when food is scarce or absent, and how to characterize individual differences in survival within a population. We use a dynamic energy budget (DEB) model to describe food acquisition, subsequent reserve dynamics and allocation of reserve to body maintenance, growth and maturation of an aquatic insect predator, Notonecta maculata. In a DEB context, we can assume that starvation-induced death strikes when the reserve of an organism is depleted to a certain extent. The way reserve dynamics change upon starvation might thereby influence the ability to survive in the absence of food. Moreover, individuals in a starved population do not die at the same time, even though they might be of the same body size with similar life histories. To describe individual differences in starvation resistance, we link the reserve dynamics derived from the DEB model to the general unified threshold model of survival (GUTS). We tested two different special cases within GUTS, individual tolerance (IT) and stochastic death (SD), and three different starvation options for their suitability in representing experimental data on body size-related starvation resistance. The DEB model reproduced laboratory data on the development of juvenile N. maculata under different food conditions well and closely predicted the weight loss of individuals during prolonged starvation. Both the combined IT-model and the combined SD-model closely fit survival for different food conditions including starvation. However, the two models make different predictions for survival under repeated transient starvation periods. Our results suggest that larger N. maculata specimens are able to resist starvation to a greater extent than smaller conspecifics. The DEB model provides a mechanistic explanation for the positive relationship between body size and starvation resistance, and offers testable hypotheses for possible deviations from this general trend. Individual organisms differ in their ability to endure transient periods of starvation with consequences for life history and population dynamics. Here, the authors provide mechanistic explanations on how survival relates to body size intraspecifically when food is scarce or totally absent, and how to characterize individual differences in survival within a population.
      PubDate: 2014-01-13T10:55:16.142392-05:
      DOI: 10.1111/1365-2656.12195
       
  • Night warming on hot days produces novel impacts on development, survival
           and reproduction in a small arthropod
    • Authors: Fei Zhao; Wei Zhang, Ary A. Hoffmann, Chun-Sen Ma
      Pages: 769 - 778
      Abstract: An asymmetric increase in night-time temperatures (NTs) on hot days is one of the main features of global climate change. But the biological effects of an increased night-time temperature combined with high daytime temperature are unclear. We used six thermal regimens to simulate NTs on hot days and investigated the effects of night warming on life-history traits of the English grain aphid Sitobion avenae. Experimental temperatures fluctuated in continuous diurnal cycles, increasing from 27 °C to a maximum 35 °C and then declining to 27 °C gradually before further dropping to different minima (13, 16, 19, 21, 23 or 25 °C) representing NTs. When compared to expectations based on constant temperatures, night warming raised the optimum temperature for development by 3 °C, in contrast to results from experiments where temperature variability was altered symmetrically or in a parallel manner. Night warming also reduced aphid survival under heat from 75% to 37% and depressed adult performance by up to 50%. Overall, night warming exacerbated the detrimental effects of hot days on the intrinsic rate of population increase, which was predicted to drop by 30% when night-time minimum temperatures exceeded 20 °C. Our novel findings on development challenge the ‘Kaufmann effect’, suggesting this is inapplicable to night warming likely to be encountered in nature. Although many average temperature models predict increasing pest outbreaks, our results suggest that outbreaks of some species might decrease due to the effects of night warming on population dynamics. Night warming often occurs in hot days under climate change. Here the authors investigate life-history traits of aphids at six night-time temperatures combined with a high daytime temperature regimen. Night warming raises optimum temperature for development which challenges the ‘Kaufmann effect’ and reduces nymphal survival unexpectedly.
      PubDate: 2014-02-25T11:46:02.878569-05:
      DOI: 10.1111/1365-2656.12196
       
  • Comparative analysis of passive defences in spiders (Araneae)
    • Authors: Stano Pekár
      Pages: 779 - 790
      Abstract: Being frequent prey of many predators, including especially wasps and birds, spiders have evolved a variety of defence mechanisms. Here I studied patterns of passive defences, namely anachoresis, crypsis, masquerade, aposematism and Batesian mimicry, in spiders. Using published information pertaining more than 1000 spider species, the phylogenetic pattern of different passive defences (i.e. defences that decrease the risk of an encounter with the predator) was investigated. Furthermore, I studied the effect of foraging guild, geographical distribution and diel activity on the frequency of defences as these determine the predators diversity, presence and perception. I found that crypsis (background matching) combined with anachoresis (hiding) was the most frequent defence confined mainly to families/genera at the base of the tree. Aposematism (warning coloration) and Batesian mimicry (imitation of noxious/dangerous model) were found in taxa that branched later in the tree, and masquerade (imitation of inedible objects) was confined to families at intermediate positions of the tree. Aposematism and Batesian mimicry were restricted to a few lineages. Masquerade was used particularly by web-building species with nocturnal activity. Aposematism was rare but mainly used by web-building diurnal species. Batesian mimicry was frequently observed in cursorial species with diurnal activity. Cryptic species were more common in temperate zones, whereas aposematic and mimetic species were more common in the tropics. Here I show that the evolution of passive defences in spiders was influenced by the ecology of species. Then, I discuss the evolutionary significance of the particularly defences. This paper presents a through analysis of various primary defences used by spiders. It shows that the type of defence used is influenced by the geographic distribution, diel activity and foraging mode. It also reveals which defences are primitive and which are advanced.
      PubDate: 2014-01-07T13:46:34.112662-05:
      DOI: 10.1111/1365-2656.12177
       
  • Spatial variation in the relationship between performance and metabolic
           rate in wild juvenile Atlantic salmon
    • Authors: Grethe Robertsen; John D. Armstrong, Keith H. Nislow, Ivar Herfindal, Simon McKelvey, Sigurd Einum
      Pages: 791 - 799
      Abstract: Maintenance of metabolic rate (MR, the energy cost of self-maintenance) is linked to behavioural traits and fitness and varies substantially within populations. Despite having received much attention, the causes and consequences of this variation remain obscure. Theoretically, such within-population variation in fitness-related traits can be maintained by environmental heterogeneity in selection patterns, but for MR, this has rarely been tested in nature. Here, we experimentally test whether the relationship between MR and performance can vary spatially by assessing survival, growth rate and movement of Atlantic salmon (Salmo salar L.) juveniles from 10 family groups differing in MR (measured as egg metabolism) that were stocked in parallel across 10 tributaries of a single watershed. The relationship between MR and relative survival and growth rate varied significantly among tributaries. Specifically, the effect of MR ranged from negative to positive for relative survival, whereas it was negative for growth rate. The association between MR and movement was positive and did not vary significantly among tributaries. These results are consistent with a fitness cost of traits associated with behavioural dominance that varies across relatively small spatial scales (within a single watershed). More generally, our results support the hypothesis that spatial heterogeneity in environmental conditions contributes to maintain within-population variation in fitness-related traits, such as MR. This is the first time survival effects of metabolic rate has been shown to vary across small spatial scales in an experimental field study, thus supporting the hypotheses that spatial heterogeneity in selection patterns can be one mechanism facilitating maintenance of intra-population variation in this fitness-related trait.
      PubDate: 2014-01-28T09:50:41.007928-05:
      DOI: 10.1111/1365-2656.12182
       
  • Anatomy of a population cycle: the role of density dependence and
           demographic variability on numerical instability and periodicity
    • Authors: Jeffrey R. Row; Paul J. Wilson, Dennis L. Murray
      Pages: 800 - 812
      Abstract: Determining the causes of cyclic fluctuations in population size is a central tenet in population ecology and provides insights into population regulatory mechanisms. We have a firm understanding of how direct and delayed density dependence affects population stability and cyclic dynamics, but there remains considerable uncertainty in the specific processes contributing to demographic variability and consequent change in cyclic propensity. Spatiotemporal variability in cyclic propensity, including recent attenuation or loss of cyclicity among several temperate populations and the implications of habitat fragmentation and climate change on this pattern, highlights the heightened need to understand processes underlying cyclic variation. Because these stressors can differentially impact survival and productivity and thereby impose variable time delays in density dependence, there is a specific need to elucidate how demographic vital rates interact with the type and action of density dependence to contribute to population stability and cyclic variation. Here, we address this knowledge gap by comparing the stability of time series derived from general and species-specific (Canada lynx: Lynx canadensis; small rodents: Microtus, Lemmus and Clethrionomys spp.) matrix population models, which vary in their demographic rates and the direct action of density dependence. Our results reveal that density dependence acting exclusively on survival as opposed to productivity is destabilizing, suggesting that a shift in the action of population regulation toward reproductive output may decrease cyclic propensity and cycle amplitude. This result was the same whether delayed density dependence was pulsatile and acted on a single time period (e.g. t−1, t−2 or t−3) vs. more constant by affecting a successive range of years (e.g. t−1,…, t−3). Consistent with our general models, reductions in reproductive potential in both the lynx and small rodent systems led to notably large drops in cyclic propensity and amplitude, suggesting that changes in this vital rate may contribute to the spatial or temporal variability observed in the cyclic dynamics of both systems. Collectively, our results reveal that the type of density dependence and its effect on different demographic parameters can profoundly influence numeric stability and cyclic propensity and therefore may shift populations across the cyclic-to-noncyclic boundary. The role of direct and delayed density dependence in generating population cyclicity are well established, but there remains uncertainty in how they interact with demographic vital rates to contribute to cyclic variation. This study reveals how the type of density dependence and its effect on demographic rates can generate spatiotemporal variation in cyclic dynamics, independent of changes in the strength of density dependence.
      PubDate: 2014-01-20T02:17:10.577441-05:
      DOI: 10.1111/1365-2656.12179
       
  • Concurrent effects of age class and food distribution on immigration
           success and population dynamics in a small mammal
    • Authors: Alice Rémy; Jean-François Galliard, Morten Odden, Harry P. Andreassen
      Pages: 813 - 822
      Abstract: During the settlement stage of dispersal, the outcome of conflicts between residents and immigrants should depend on the social organization of resident populations as well as on individual traits of immigrants, such as their age class, body mass and/or behaviour. We have previously shown that spatial distribution of food influences the social organization of female bank voles (Myodes glareolus). Here, we aimed to determine the relative impact of food distribution and immigrant age class on the success and demographic consequences of female bank vole immigration. We manipulated the spatial distribution of food within populations having either clumped or dispersed food. After a pre-experimental period, we released either adult immigrants or juvenile immigrants, for which we scored sociability and aggressiveness prior to introduction. We found that immigrant females survived less well and moved more between populations than resident females, which suggest settlement costs. However, settled juvenile immigrants had a higher probability to reproduce than field-born juveniles. Food distribution had little effects on the settlement success of immigrant females. Survival and settlement probabilities of immigrants were influenced by adult female density in opposite ways for adult and juvenile immigrants, suggesting a strong adult–adult competition. Moreover, females of higher body mass at release had a lower probability to survive, and the breeding probability of settled immigrants increased with their aggressiveness and decreased with their sociability. Prior to the introduction of immigrants, resident females were more aggregated in the clumped food treatment than in the dispersed food treatment, but immigration reversed this relationship. In addition, differences in growth trajectories were seen during the breeding season, with populations reaching higher densities when adult immigrants were introduced in a plot with dispersed food, or when juvenile immigrants were introduced in a plot with clumped food. These results indicate the relative importance of intrinsic and extrinsic factors on immigration success and demographic consequences of dispersal and are of relevance to conservation actions, such as reinforcement of small populations. The authors test, for the first time, the concurrent effects of the spatial distribution of food and immigrant age class on the success and impact of immigration. The results suggest that different individual traits are involved at different stages of the immigration process and that demographic consequences of immigration are context dependent.
      PubDate: 2014-02-03T23:03:34.700657-05:
      DOI: 10.1111/1365-2656.12184
       
  • The invasion of southern South America by imported bumblebees and
           associated parasites
    • Authors: Regula Schmid-Hempel; Michael Eckhardt, David Goulson, Daniel Heinzmann, Carlos Lange, Santiago Plischuk, Luisa R. Escudero, Rahel Salathé, Jessica J. Scriven, Paul Schmid-Hempel
      Pages: 823 - 837
      Abstract: The Palaearctic Bombus ruderatus (in 1982/1983) and Bombus terrestris (1998) have both been introduced into South America (Chile) for pollination purposes. We here report on the results of sampling campaigns in 2004, and 2010–2012 showing that both species have established and massively expanded their range. Bombus terrestris, in particular, has spread by some 200 km year−1 and had reached the Atlantic coast in Argentina by the end of 2011. Both species, and especially B. terrestris, are infected by protozoan parasites that seem to spread along with the imported hosts and spillover to native species. Genetic analyses by polymorphic microsatellite loci suggest that the host population of B. terrestris is genetically diverse, as expected from a large invading founder population, and structured through isolation by distance. Genetically, the populations of the trypanosomatid parasite, Crithidia bombi, sampled in 2004 are less diverse, and distinct from the ones sampled later. Current C. bombi populations are highly heterozygous and also structured through isolation by distance correlating with the genetic distances of B. terrestris, suggesting the latter's expansion to be a main structuring factor for the parasite. Remarkably, wherever B. terrestris spreads, the native Bombus dahlbomii disappears although the reasons remain unclear. Our ecological and genetic data suggest a major invasion event that is currently unfolding in southern South America with disastrous consequences for the native bumblebee species. This study documents how two species of bumblebees have spread since their introduction, what parasites they carry, and what their genetic population structure is. Taken together, the data show an unprecedented, very rapid invasive spread of one species, probably facilitated by associated parasites. The geographical scale of this invasion event affects the entire southern half of South America (B. dahlbomii, photograph P. Schmid-Hempel).
      PubDate: 2014-01-29T13:27:56.173344-05:
      DOI: 10.1111/1365-2656.12185
       
  • Warmer temperatures increase disease transmission and outbreak intensity
           in a host–pathogen system
    • Authors: Bret D. Elderd; James R. Reilly
      Pages: 838 - 849
      Abstract: While rising global temperatures are increasingly affecting both species and their biotic interactions, the debate about whether global warming will increase or decrease disease transmission between individuals remains far from resolved. This may stem from the lack of empirical data. Using a tractable and easily manipulated insect host–pathogen system, we conducted a series of field and laboratory experiments to examine how increased temperatures affect disease transmission using the crop-defoliating pest, the fall armyworm (Spodoptera frugiperda) and its species-specific baculovirus, which causes a fatal infection. To examine the effects of temperature on disease transmission in the field, we manipulated baculovirus density and temperature. As infection occurs when a host consumes leaf tissue on which the pathogen resides, baculovirus density was controlled by placing varying numbers of infected neonate larvae on experimental plants. Temperature was manipulated by using open-top chambers (OTCs). The laboratory experiments examined how increased temperatures affect fall armyworm feeding and development rates, which provide insight into how host feeding behaviour and physiology may affect transmission. Disease transmission and outbreak intensity, measured as the cumulative fraction infected during an epizootic, increased at higher temperatures. However, there was no appreciable change in the mean transmission rate of the disease, which is often the focus of empirical and theoretical research. Instead, the coefficient of variation (CV) associated with the transmission rate shrunk. As the CV decreased, heterogeneity in disease risk across individuals declined, which resulted in an increase in outbreak intensity. In the laboratory, increased temperatures increased feeding rates and decreased developmental times. As the host consumes the virus along with the leaf tissue on which it resides, increased feeding rate is likely to increase the probability of an individual consuming virus-infected leaf tissue. On the other hand, decreased developmental time increases the sloughing of midgut cells, which is predicted to hinder viral infection. Increases in outbreak intensity or epizootic severity, as the climate warms, may lead to changes in the long-term dynamics of pests whose populations are strongly affected by host–pathogen interactions. Overall, this work demonstrates that the usual assumptions governing these effects, via changes in the mean transmission rate alone, may not be correct. The effects of climate change on disease transmission usually involve examining differences in transmission rates under various temperature regimes. Using empirical data from a field experiment, the authors show that variability about the rate of transmission may be equally if not more important when considering global warming.
      PubDate: 2014-01-06T13:00:54.329331-05:
      DOI: 10.1111/1365-2656.12180
       
  • Natural malaria infection reduces starvation resistance of nutritionally
           stressed mosquitoes
    • Authors: Fabrice Lalubin; Aline Delédevant, Olivier Glaizot, Philippe Christe
      Pages: 850 - 857
      Abstract: In disease ecology, there is growing evidence that environmental quality interacts with parasite and host to determine host susceptibility to an infection. Most studies of malaria parasites have focused on the infection costs incurred by the hosts, and few have investigated the costs on mosquito vectors. The interplay between the environment, the vector and the parasite has therefore mostly been ignored and often relied on unnatural or allopatric Plasmodium/vector associations. Here, we investigated the effects of natural avian malaria infection on both fecundity and survival of field-caught female Culex pipiens mosquitoes, individually maintained in laboratory conditions. We manipulated environmental quality by providing mosquitoes with different concentrations of glucose-feeding solution prior to submitting them to a starvation challenge. We used molecular-based methods to assess mosquitoes’ infection status. We found that mosquitoes infected with Plasmodium had lower starvation resistance than uninfected ones only under low nutritional conditions. The effect of nutritional stress varied with time, with the difference of starvation resistance between optimally and suboptimally fed mosquitoes increasing from spring to summer, as shown by a significant interaction between diet treatment and months of capture. Infected and uninfected mosquitoes had similar clutch size, indicating no effect of infection on fecundity. Overall, this study suggests that avian malaria vectors may suffer Plasmodium infection costs in their natural habitat, under certain environmental conditions. This may have major implications for disease transmission in the wild. The authors find, for the first time using a natural avian malaria model system, that naturally infected mosquitoes suffered reduced survival only under nutritionally stressing conditions. Hence, glucose availability may likely shape the vectorial capacity of mosquitoes in their natural habitat – a result of significant importance for epidemiology and the control of malaria.
      PubDate: 2014-01-06T13:01:00.120756-05:
      DOI: 10.1111/1365-2656.12190
       
  • Multiple aspects of plasticity in clutch size vary among populations of a
           globally distributed songbird
    • Authors: David F. Westneat; Veronika Bókony, Terry Burke, Olivier Chastel, Henrik Jensen, Thomas Kvalnes, Ádám Z. Lendvai, András Liker, Douglas Mock, Julia Schroeder, P. L. Schwagmeyer, Gabriele Sorci, Ian R. K. Stewart
      Pages: 876 - 887
      Abstract: Plasticity in life-history characteristics can influence many ecological and evolutionary phenomena, including how invading organisms cope with novel conditions in new locations or how environmental change affects organisms in native locations. Variation in reaction norm attributes is a critical element to understanding plasticity in life history, yet we know relatively little about the ways in which reaction norms vary within and among populations. We amassed data on clutch size from marked females in eight populations of house sparrows (Passer domesticus) from North America and Europe. We exploited repeated measures of clutch size to assess both the extent of within-individual phenotypic plasticity and among-individual variation and to test alternative hypotheses about the underlying causes of reaction norm shape, particularly the decline in clutch size with date. Across all populations, females of this multibrooded species altered their clutch size with respect to date, attempt order, and the interaction of date and order, producing a reaction norm in multidimensional environmental space. The reaction norm fits that predicted by a model in which optimal clutch size is driven by a decline with date hatched in the ability of offspring to recruit. Our results do not fit those predicted for other proposed causes of a seasonal decline in clutch size. We also found significant differences between populations in response to date and the date by attempt order interaction. We tested the prediction that the relationship with date should be increasingly negative as breeding season becomes shorter but found steeper declines in clutch size with date in populations with longer seasons, contrary to the prediction. Populations also differed in the level of among-individual variation in reaction norm intercept, but we found no evidence of among-individual variation in reaction norm slope. We show that complex reaction norms in life-history characters exhibit within- and among-population variance. The nature of this variance is only partially consistent with current life-history theory and stimulates expansions of such theory to accommodate complexities in adaptive life history. Here, the authors describe a complex pattern of within-individual flexibility in house sparrow clutch size. Particular aspects of flexibility vary among populations, but not as predicted by life-history theory. This has implications for understanding plasticity in life-history traits in general, and hypotheses about clutch size in particular. Photo credit to H. Jensen.
      PubDate: 2014-02-07T08:28:42.447961-05:
      DOI: 10.1111/1365-2656.12191
       
  • Experimentally decoupling reproductive investment from energy storage to
           test the functional basis of a life-history trade-off
    • Authors: Robert M. Cox; Matthew B. Lovern, Ryan Calsbeek
      Pages: 888 - 898
      Abstract: The ubiquitous life-history trade-off between reproduction and survival has long been hypothesized to reflect underlying energy-allocation trade-offs between reproductive investment and processes related to self-maintenance. Although recent work has questioned whether energy-allocation models provide sufficient explanations for the survival cost of reproduction, direct tests of this hypothesis are rare, especially in wild populations. This hypothesis was tested in a wild population of brown anole lizards (Anolis sagrei) using a two-step experiment. First, stepwise variation in reproductive investment was created using unilateral and bilateral ovariectomy (OVX) along with intact (SHAM) control. Next, this manipulation was decoupled from its downstream effects on energy storage by surgically ablating the abdominal fat stores from half of the females in each reproductive treatment. As predicted, unilateral OVX (intermediate reproductive investment) induced levels of growth, body condition, fat storage and breeding-season survival that were intermediate between the high levels of bilateral OVX (no reproductive investment) and the low levels of SHAM (full reproductive investment). Ablation of abdominal fat bodies had a strong and persistent effect on energy stores, but it did not influence post-breeding survival in any of the three reproductive treatments. This suggests that the energetic savings of reduced reproductive investment do not directly enhance post-breeding survival, with the caveat that only one aspect of energy storage was manipulated and OVX itself had no overall effect on post-breeding survival. This study supports the emerging view that simple energy-allocation models may often be insufficient as explanations for the life-history trade-off between reproduction and survival. This study uses a unique experimental design to alter reproductive investment and then decouple this manipulation from its downstream effects on energy storage in a wild lizard population. The results challenge the common assumption that life-history trade-offs between reproduction and survival arise from underlying energy-allocation trade-offs.
      PubDate: 2014-05-13T14:19:30.795216-05:
      DOI: 10.1111/1365-2656.12228
       
  • Do stage-specific functional responses of consumers dampen the effects of
           subsidies on trophic cascades in streams'
    • Authors: Takuya Sato; Katsutoshi Watanabe
      Pages: 907 - 915
      Abstract: Resource subsidies often weaken trophic cascades in recipient communities via consumers' functional response to the subsidies. Consumer populations are commonly stage-structured and may respond to the subsidies differently among the stages yet less is known about how this might impact the subsidy effects on the strength of trophic cascades in recipient systems. We show here, using a large-scale field experiment, that the stage structure of a recipient consumer would dampen the effects of terrestrial invertebrate subsidies on the strength of trophic cascade in streams. When a high input rate of the terrestrial invertebrates was available, both large and small fish stages switched their diet to the terrestrial subsidy, which weakened the trophic cascade in streams. However, when the input rate of the terrestrial invertebrates was at a moderate level, the terrestrial subsidy did not weaken the trophic cascade. This discrepancy was likely due to small fish stages being competitively excluded from feeding on the subsidy by larger stages of fish and primarily foraging on benthic invertebrates under the moderate input level. Although previous studies using single fish stages have clearly demonstrated that the terrestrial invertebrate input equivalent to our moderate input rate weakened the trophic cascade in streams, this subsidy effect might be overestimated given small fish stage may not switch their diet to the subsidy under competition with large fish stage. Given the ubiquity of consumer stage structure and interaction among consumer stages, the effects we saw might be widespread in nature, requiring future studies that explicitly involve consumer's stage structure into community ecology. This is the first and novel study showing how the stage-specific functional responses of consumers are important to determine the strength of trophic cascade in the ecosystems that receive resource subsidies.
      PubDate: 2014-02-05T11:45:40.331396-05:
      DOI: 10.1111/1365-2656.12192
       
  • Towards an energetic landscape: broad-scale accelerometry in woodland
           caribou
    • Authors: Anna A. Mosser; Tal Avgar, Glen S. Brown, C. Spencer Walker, John M. Fryxell
      Pages: 916 - 922
      Abstract: Energetic balance is a central driver of individual survival and population change, yet estimating energetic costs in free- and wide-ranging animals presents a significant challenge. Animal-borne activity monitors (using accelerometer technology) present a promising method of meeting this challenge and open new avenues for exploring energetics in natural settings. To determine the behaviours and estimated energetic costs associated with a given activity level, three captive reindeer (Rangifer tarandus tarandus) at the Toronto Zoo were fitted with collars and observed for 53 h. Activity patterns were then measured over 13 months for 131 free-ranging woodland caribou (R. t. caribou) spanning 450 000 km2 in northern Ontario. The captive study revealed a positive but decelerating relationship between activity level and energetic costs inferred from previous behavioural studies. Field-based measures of activity were modelled against individual displacement, vegetation abundance (Normalized Difference Vegetation Index), snow depth and temperature, and the best fit model included all parameters and explained over half of the variation in the data. Individual displacement was positively related to activity levels, suggesting that broad differences in energetic demands are influenced by variation in movement rates. After accounting for displacement, activity was highest at intermediate levels of vegetation abundance, presumably due to foraging behaviour. Snow depth, probably associated with digging for winter forage, moderately increased activity. Activity levels increased significantly at the coldest winter temperatures, suggesting the use of behavioural thermoregulation by caribou. These interpretations of proximate causal factors should be regarded as hypotheses subject to validation under normal field conditions. These results illustrate the landscape characteristics that increase energetic demands for caribou and confirm the great potential for the use of accelerometry in studies of animal energetics. One of the most difficult challenges in ecology is understanding the costs and benefits for animals living in complex landscapes under highly variable environmental conditions. Here, the authors show how accelerometers attached to radiocollars can be used to assess spatial and temporal variation in energetic costs facing free-ranging caribou in Canada's boreal forest.
      PubDate: 2014-03-14T11:03:14.466643-05:
      DOI: 10.1111/1365-2656.12187
       
  • Behavioural and physiological responses of limpet prey to a seastar
           predator and their transmission to basal trophic levels
    • Authors: Tatiana Manzur; Francisco Vidal, José F. Pantoja, Miriam Fernández, Sergio A. Navarrete
      Pages: 923 - 933
      Abstract: Besides the well-documented behavioural changes induced by predators on prey, predator-induced stress can also include a suite of biochemical, neurological and metabolic changes that may represent important energetic costs and have long-lasting effects on individuals and on the demography of prey populations. The rapid transmission of prey behavioural changes to lower trophic levels, usually associated with alteration of feeding rates, can substantially change and even reverse direction over the long term as prey cope with the energetic costs associated with predation-induced stress. It is therefore critical to evaluate different aspects and assess the costs of non-consumptive predator effects on prey. We investigated the behavioural and physiological responses of an herbivorous limpet, Fissurella limbata, to the presence of chemical cues and direct non-lethal contact by the common seastar predator, Heliaster helianthus. We also evaluated whether the limpets feeding behaviour was modified by the predator and whether this translated into positive or negative effects on biomass of the green alga, Ulva sp. Our experimental results show the presence of Heliaster led to increased movement activity, increased distances travelled, changes in time budget over different environmental conditions and increased feeding rate in the keyhole limpets. Moreover, additional experiments showed that, beyond the increased metabolic rate associated with limpet increased activity, predator chemical cues heighten metabolic rate as part of the induced stress response. Changes in individual movement and displacement distances observed through the 9-day experiment can be interpreted as part of the escape response exhibited by limpets to reduce the risk of being captured by the predator. Increased limpet feeding rate on algae can be visualized as a way individuals compensate for the elevated energetic costs of movement and heightened metabolic rates produced by the predator-induced stress, which can lead to negative effects on abundance of the lower trophic level. We suggest that in order to understand the total non-consumptive effect of predators in natural communities, it is necessary to evaluate not only short-term behavioural responses, but also the costs associated with the multiple interdependent pathways triggered by predator-induced stress, and determine how individuals cope with these costs in the long term. In an intertidal predator–prey system, the authors investigate the interplay among behavioural and physiological responses to predator-induced stress, demonstrating important energetic costs that can have long-lasting effects and can be transferred through the community.
      PubDate: 2014-02-25T11:46:05.639677-05:
      DOI: 10.1111/1365-2656.12199
       
  • Revisiting food-based models of territoriality in solitary predators
    • Authors: José V. López-Bao; Alejandro Rodríguez, Miguel Delibes, José M. Fedriani, Javier Calzada, Pablo Ferreras, Francisco Palomares
      Pages: 934 - 942
      Abstract: Food availability is considered a major factor determining spacing behaviour in territorial species, especially for females. Theoretically, spatial overlap (considered the opposite of territoriality) and food availability are related in a nonlinear manner (hypothesized inverted-U function), with high overlap levels at the extremes of a food availability gradient and low overlap at intermediate levels of this gradient. Similar patterns are expected for encounter frequencies owing to its expected correlation with spatial overlap. However, these predictions have rarely been tested in highly structured social systems on a broad gradient of food availability, which implicitly requires experimental manipulation. We test these predictions in a solitary, territorial and trophic specialist, the Iberian lynx Lynx pardinus, taking advantage of a three-decade data set of spatial behaviour in different scenarios of food availability (i.e. rabbit density). In contrast with expectations, home range overlap among resident females was low (median overlap index = 0·08, range 0–0·57) and core area overlap was nearly nil (median overlap index = 0, range 0–0·22) throughout the entire gradient of prey availability. Furthermore, spatial associations between pairs of females were negligible regardless marked variation in prey availability. Therefore, we did not find support for a model of flexible lynx territoriality driven by food availability. Our results suggest that the exclusive use of space in the Iberian lynx was not related to food. Lack of influence of prey availability on lynx territoriality may be adaptive to cope with the consequences of frequent drought-induced periods of prey scarcity or other disturbance typically affecting wild rabbit populations in Mediterranean environments. Thus, lynx would adopt an obstinate strategy of territoriality that consists in defending exclusive areas across a broad range of resource availability ensuring an exclusive access to the minimum amount of prey necessary for survival and eventually reproduction even during periods of prey scarcity. However, we found signs that territoriality was influenced by lynx density in a nonlinear fashion. Our results suggest the occurrence of population regulation through territoriality in this species. This paper shows that territoriality in the Iberian lynx is not related to food. Lynx adopt an obstinate strategy of territoriality consisting in defending exclusive areas across a broad prey availability gradient. The authors suggest the occurrence of population regulation through territoriality.
      PubDate: 2014-05-13T14:57:44.782489-05:
      DOI: 10.1111/1365-2656.12226
       
  • Niche filtering rather than partitioning shapes the structure of temperate
           forest ant communities
    • Authors: David Fowler; Jean-Philippe Lessard, Nathan J. Sanders
      Pages: 943 - 952
      Abstract: An ever-increasing number of studies use tools from community phylogenetics to infer the processes underlying the assembly of communities. However, very few studies simultaneously use experimental approaches to characterize the ecological niches of species and directly assess the importance of these structuring processes. In this study, we developed an experimental approach for quantifying the use of four types of food resources and three habitat templets in temperate forest ant assemblages. We then used null models to assess whether niches overlapped more or less than expected by chance. Finally, we integrated comparative phylogenetic methods with experimental data on niche use to assess the degree of phylogenetic signal in several key components of the niche. We found that niche filtering, rather than partitioning, was the predominant structuring force. Niche filtering resulted from conservatism in habitat niches in evolutionary time and limitations in the availability of food resources in ecological time. Our study thus supports the idea that similarities in niches among species, rather than the differences, drive the assembly of ant communities. This work combines experimental, phylogenetic and null modelling approaches to ask an age-old question: How do species co-occur at the same place at the same time' The experiments were carried out in forest sites such as this one in southern Appalachia.
      PubDate: 2014-01-29T13:27:18.934487-05:
      DOI: 10.1111/1365-2656.12188
       
  • Predator effects on a detritus-based food web are primarily mediated by
           non-trophic interactions
    • Authors: Nabil Majdi; Anatole Boiché, Walter Traunspurger, Antoine Lecerf
      Pages: 953 - 962
      Abstract: Predator effects on ecosystems can extend far beyond their prey and are often not solely lethally transmitted. Change in prey traits in response to predation risk can have important repercussions on community assembly and key ecosystem processes (i.e. trait-mediated indirect effects). In addition, some predators themselves alter habitat structure or nutrient cycling through ecological engineering effects. Tracking these non-trophic pathways is thus an important, yet challenging task to gain a better grasp of the functional role of predators. Multiple lines of evidence suggest that, in detritus-based food webs, non-trophic interactions may prevail over purely trophic interactions in determining predator effects on plant litter decomposition. This hypothesis was tested in a headwater stream by modulating the density of a flatworm predator (Polycelis felina) in enclosures containing oak (Quercus robur) leaf litter exposed to natural colonization by small invertebrates and microbial decomposers. Causal path modelling was used to infer how predator effects propagated through the food web. Flatworms accelerated litter decomposition through positive effects on microbial decomposers. The biomass of prey and non-prey invertebrates was not negatively affected by flatworms, suggesting that net predator effect on litter decomposition was primarily determined by non-trophic interactions. Flatworms enhanced the deposition and retention of fine sediments on leaf surface, thereby improving leaf colonization by invertebrates – most of which having strong affinities with interstitial habitats. This predator-induced improvement of habitat availability was attributed to the sticky nature of the mucus that flatworms secrete in copious amount while foraging. Results of path analyses further indicated that this bottom-up ecological engineering effect was as powerful as the top-down effect on invertebrate prey. Our findings suggest that predators have the potential to affect substantially carbon flow and nutrient cycling in detritus-based ecosystems and that this impact cannot be fully appreciated without considering non-trophic effects. The authors show experimentally that non-trophic effects override lethally transmitted top-down predator impacts on an aquatic detritus-based ecosystem. Specifically, the results hint at interesting mechanisms by which the predatory flatworm Polycelis felina enhances detritus processing and colonization.
      PubDate: 2014-01-29T13:27:37.910282-05:
      DOI: 10.1111/1365-2656.12189
       
  • The marine diversity spectrum
    • Authors: Daniel C. Reuman; Henrik Gislason, Carolyn Barnes, Frédéric Mélin, Simon Jennings
      Pages: 963 - 979
      Abstract: Distributions of species body sizes within a taxonomic group, for example, mammals, are widely studied and important because they help illuminate the evolutionary processes that produced these distributions. Distributions of the sizes of species within an assemblage delineated by geography instead of taxonomy (all the species in a region regardless of clade) are much less studied but are equally important and will illuminate a different set of ecological and evolutionary processes. We develop and test a mechanistic model of how diversity varies with body mass in marine ecosystems. The model predicts the form of the ‘diversity spectrum’, which quantifies the distribution of species' asymptotic body masses, is a species analogue of the classic size spectrum of individuals, and which we have found to be a new and widely applicable description of diversity patterns. The marine diversity spectrum is predicted to be approximately linear across an asymptotic mass range spanning seven orders of magnitude. Slope −0·5 is predicted for the global marine diversity spectrum for all combined pelagic zones of continental shelf seas, and slopes for large regions are predicted to lie between −0·5 and −0·1. Slopes of −0·5 and −0·1 represent markedly different communities: a slope of −0·5 depicts a 10-fold reduction in diversity for every 100-fold increase in asymptotic mass; a slope of −0·1 depicts a 1·6-fold reduction. Steeper slopes are predicted for larger or colder regions, meaning fewer large species per small species for such regions. Predictions were largely validated by a global empirical analysis. Results explain for the first time a new and widespread phenomenon of biodiversity. Results have implications for estimating numbers of species of small asymptotic mass, where taxonomic inventories are far from complete. Results show that the relationship between diversity and body mass can be explained from the dependence of predation behaviour, dispersal, and life history on body mass, and a neutral assumption about speciation and extinction. This work demonstrates and explains for the first time a global phenomenon of how species diversity varies with body size in marine systems.
      PubDate: 2014-03-03T10:05:47.986948-05:
      DOI: 10.1111/1365-2656.12194
       
  • Spatial analyses for nonoverlapping objects with size variations and their
           application to coral communities
    • Authors: Soyoka Muko; Ichiro K. Shimatani, Yoko Nozawa
      Pages: 980 - 990
      Abstract: Spatial distributions of individuals are conventionally analysed by representing objects as dimensionless points, in which spatial statistics are based on centre-to-centre distances. However, if organisms expand without overlapping and show size variations, such as is the case for encrusting corals, interobject spacing is crucial for spatial associations where interactions occur. We introduced new pairwise statistics using minimum distances between objects and demonstrated their utility when examining encrusting coral community data. We also calculated the conventional point process statistics and the grid-based statistics to clarify the advantages and limitations of each spatial statistical method. For simplicity, coral colonies were approximated by disks in these demonstrations. Focusing on short-distance effects, the use of minimum distances revealed that almost all coral genera were aggregated at a scale of 1–25 cm. However, when fragmented colonies (ramets) were treated as a genet, a genet-level analysis indicated weak or no aggregation, suggesting that most corals were randomly distributed and that fragmentation was the primary cause of colony aggregations. In contrast, point process statistics showed larger aggregation scales, presumably because centre-to-centre distances included both intercolony spacing and colony sizes (radius). The grid-based statistics were able to quantify the patch (aggregation) scale of colonies, but the scale was strongly affected by the colony size. Our approach quantitatively showed repulsive effects between an aggressive genus and a competitively weak genus, while the grid-based statistics (covariance function) also showed repulsion although the spatial scale indicated from the statistics was not directly interpretable in terms of ecological meaning. The use of minimum distances together with previously proposed spatial statistics helped us to extend our understanding of the spatial patterns of nonoverlapping objects that vary in size and the associated specific scales. New pairwise statistics using minimum distances between objects are introduced to analyse the spatial patterns of nonoverlapping objects that vary in size. The utility is demonstrated by comparison with the conventional point process statistics and the grid-based statistics applied to encrusting coral community data.
      PubDate: 2014-02-22T02:10:19.929228-05:
      DOI: 10.1111/1365-2656.12193
       
  • Large-scale movements in European badgers: has the tail of the movement
           kernel been underestimated'
    • Authors: Andrew W. Byrne; John L. Quinn, James J. O'Keeffe, Stuart Green, D. Paddy Sleeman, S. Wayne Martin, John Davenport
      Pages: 991 - 1001
      Abstract: Characterizing patterns of animal movement is a major aim in population ecology, and yet doing so at an appropriate spatial scale remains a major challenge. Estimating the frequency and distances of movements is of particular importance when species are implicated in the transmission of zoonotic diseases. European badgers (Meles meles) are classically viewed as exhibiting limited dispersal, and yet their movements bring them into conflict with farmers due to their potential to spread bovine tuberculosis in parts of their range. Considerable uncertainty surrounds the movement potential of badgers, and this may be related to the spatial scale of previous empirical studies. We conducted a large-scale mark–recapture study (755 km2; 2008–2012; 1935 capture events; 963 badgers) to investigate movement patterns in badgers, and undertook a comparative meta-analysis using published data from 15 European populations. The dispersal movement (>1 km) kernel followed an inverse power-law function, with a substantial ‘tail’ indicating the occurrence of rare long-distance dispersal attempts during the study period. The mean recorded distance from this distribution was 2·6 km, the 95 percentile was 7·3 km and the longest recorded was 22·1 km. Dispersal frequency distributions were significantly different between genders; males dispersed more frequently than females, but females made proportionally more long-distance dispersal attempts than males. We used a subsampling approach to demonstrate that the appropriate minimum spatial scale to characterize badger movements in our study population was 80 km2, substantially larger than many previous badger studies. Furthermore, the meta-analysis indicated a significant association between maximum movement distance and study area size, while controlling for population density. Maximum long-distance movements were often only recorded by chance beyond the boundaries of study areas. These findings suggest that the tail of the badger movement distribution is currently underestimated. The implications of this for understanding the spatial ecology of badger populations and for the design of disease intervention strategies are potentially significant. Here, badger movements were studied at the largest spatial-scale hitherto undertaken (755 km2). The authors found that badger movements were characterised by a power-law distribution, and that spatial-scale had an important influence on movement estimation. A meta-analysis suggested that long-distance movements have been previously underestimated in this species.
      PubDate: 2014-03-06T13:47:22.431261-05:
      DOI: 10.1111/1365-2656.12197
       
  • Dispersal, niche breadth and population extinction: colonization ratios
           predict range size in North American dragonflies
    • Authors: Shannon J. McCauley; Christopher J. Davis, Earl E. Werner, Michael S. Robeson
      Pages: 858 - 865
      Abstract: Species' range sizes are shaped by fundamental differences in species' ecological and evolutionary characteristics, and understanding the mechanisms determining range size can shed light on the factors responsible for generating and structuring biological diversity. Moreover, because geographic range size is associated with a species' risk of extinction and their ability to respond to global changes in climate and land use, understanding these mechanisms has important conservation implications. Despite the hypotheses that dispersal behaviour is a strong determinant of species range areas, few data are available to directly compare the relationship between dispersal behaviour and range size. Here, we overcome this limitation by combining data from a multispecies dispersal experiment with additional species-level trait data that are commonly hypothesized to affect range size (e.g. niche breadth, local abundance and body size.). This enables us to examine the relationship between these species-level traits and range size across North America for fifteen dragonfly species. Ten models based on a priori predictions about the relationship between species traits and range size were evaluated and two models were identified as good predictors of species range size. These models indicated that only two species' level traits, dispersal behaviour and niche breadth were strongly related to range size. The evidence from these two models indicated that dragonfly species that disperse more often and further had larger North American ranges. Extinction and colonization dynamics are expected to be a key linkage between dispersal behaviour and range size in dragonflies. To evaluate how extinction and colonization dynamics among dragonflies were related to range size we used an independent data set of extinction and colonization rates for eleven dragonfly species and assessed the relationship between these populations rates and North American range areas for these species. We found a negative relationship between North American range size and species' extinction-to-colonization ratios. Our results indicate that metapopulation dynamics act to shape the extent of species' continental distributions. These population dynamics are likely to interact with dispersal behaviour, particularly at species range margins, to determine range limits and ultimately species range sizes. Species range size affects their risk of extinction and can shape their response to climate change. This study of range size in dragonflies reveals that species traits and population dynamics are related to their range size, more dispersive species and those with higher colonization to extinction ratios had larger ranges.
      PubDate: 2013-12-10T05:24:52.059001-05:
      DOI: 10.1111/1365-2656.12181
       
  • Temperature-related variation in growth rate, size, maturation and life
           span in a marine herbivorous fish over a latitudinal gradient
    • Authors: Elizabeth D. L. Trip; Kendall D. Clements, David Raubenheimer, J. Howard Choat
      Pages: 866 - 875
      Abstract: In ectotherms, growth rate, body size and maturation rate covary with temperature, with the direction and magnitude of variation predicted by the Temperature-Size Rule (TSR). Nutritional quality or availability of food, however, may vary over latitudinal gradients, resulting in ambiguous effects on body size and maturation rate. The Temperature-Constraint Hypothesis (TCH) predicts that marine herbivorous ectotherms are nutritionally compromised at latitudes exceeding 30°. This provides an opportunity to resolve the contrasting demographic responses of ectotherms to variation in temperature and nutritional status over latitudinal gradients. This study uses analysis of demographic rates to evaluate the predictions of the TSR in a marine herbivorous ectotherm sampled over a significant latitudinal gradient. The direction and magnitude of demographic variation was established in the marine herbivorous fish, Odax pullus (the butterfish), and compared with that of a phylogenetically related but trophically distinct species, the carnivorous Notolabrus fucicola (the banded wrasse). Both species were sampled at three locations across the length of New Zealand covering latitudes between 35°S and 49°S. Growth rate, mean size-at-age, age- and size-at-maturity, life span and abundance were estimated for each species at each location. Demographic traits of both taxa varied with latitude. Both species showed slower initial growth rates, and matured later at a larger body size at higher latitudes than populations sampled at lower latitudes. In addition, abundances increased significantly at higher latitudes in both species. These results were consistent with the TSR but not with the TCH, confirming that nutritional ecology (herbivore vs. carnivory) did not determine demographic patterns over a biologically significant latitudinal gradient. Results from this study suggest that the absence of herbivorous reef fishes from the higher latitudes of the Northern Hemisphere may not reflect a general physiological mechanism as suggested by the TCH and highlights the need to clarify the evolutionary histories of the marine biota of each hemisphere. A long-standing hypothesis predicts that marine piscine herbivory is restricted to warmer latitudes. This study shows that temperature, not nutritional ecology, has a pervasive influence on the demography of a marine herbivorous fish and argues against the hypothesis that marine herbivorous fishes are nutritionally compromised at latitudes exceeding 30°.
      PubDate: 2013-12-10T05:32:29.753719-05:
      DOI: 10.1111/1365-2656.12183
       
  • Inducible offences affect predator–prey interactions and
           life-history plasticity in both predators and prey
    • Authors: Osamu Kishida; Zacharia Costa, Ayumi Tezuka, Hirofumi Michimae
      Pages: 899 - 906
      Abstract: Phenotypic plasticity can have strong impacts on predator–prey interactions. Although much work has examined the effects of inducible defences, less understood is how inducible offences in predators affect predator–prey interactions and predator and prey phenotypes. Here, we examine the impacts of an inducible offence on the interactions and life histories of a cohort of predatory Hynobius retardatus salamander larvae and their prey, Rana pirica tadpoles. We examined larval (duration, survival) and post-metamorphic (size) traits of both species after manipulating the presence/absence of tadpoles and salamanders with offensive (broadened gape width) or non-offensive phenotypes in pond enclosures. Offensive phenotype salamanders reduced tadpole survival and metamorph emergence by 58% compared to tadpole-only treatments, and by over 30% compared to non-offensive phenotypes. Average time to metamorphosis of frogs was delayed by 30% in the presence of salamanders, although this was independent of salamander phenotype. Thus, offensive phenotype salamanders reduced the number of tadpoles remaining in the pond over time by reducing tadpole survival, not by altering patterns of metamorph emergence. Offensive phenotypes also caused tadpoles to metamorphose 19% larger than no salamander treatments and 6% larger than non-offensive phenotype treatments. Pooled across salamander treatments, tadpoles caused salamanders to reach metamorphosis faster and larger. Moreover, in the presence of tadpoles, offensive phenotype salamanders metamorphosed 25% faster and 5% larger than non-offensive phenotype salamanders, but in their absence, neither their size nor larval period differed from non-offensive phenotype individuals. To our knowledge, this study is the first to demonstrate that inducible offences in predators can have strong impacts on predator and prey phenotypes across multiple life stages. Since early metamorphosis at a larger size has potential fitness advantages, the impacts of offensive phenotypes on frog and salamander life histories likely have significant consequences for individuals and populations. Furthermore, increased predation on tadpoles likely causes offensive phenotype individuals to have strong impacts on pond communities. Future studies should examine the fitness consequences of morphological and life-history plasticity across multiple life stages and should address the population and community level consequences of offensive phenotypes. Trait changes in predator individuals, inducible offences, are well known examples of phenotypic plasticity, but less understood is how inducible offences affect predator-prey interactions. This study demostrates that inducible offences of predatory salamanders (Hynobius retardatus) have strong impacts on trophic interaction and predator and prey phenotypes across multiple life stages. Photo is a H. retardatus salsamander larva with offensive phenotype in a natural pond.
      PubDate: 2013-12-09T13:05:17.956557-05:
      DOI: 10.1111/1365-2656.12186
       
  • Long‐term phenological trends, species accumulation rates, aphid
           traits and climate: five decades of change in migrating aphids.
    • Abstract: 1. Aphids represent a significant challenge to food production. The Rothamsted Insect Survey (RIS) runs a network of 12.2m suction‐traps throughout the year to collect migrating aphids. In 2014 the RIS celebrated its 50th anniversary. This paper marks that achievement with an extensive spatio‐temporal analysis and the provision of the first British annotated checklist of aphids since 1964. 2. Our main aim was to elucidate mechanisms that advance aphid phenology under climate change and explain these using life history traits. We then highlight emerging pests using accumulation patterns. 3. Linear and non‐linear mixed‐effect models estimated the average rate of change per annum and effects of climate on annual counts, first and last flights and length of flight season since 1965. Two climate drivers were used: the accumulated day degrees above 16°C (ADD16) indicated the potential for migration during the aphid season; the North Atlantic Oscillation (NAO) signalled the severity of the winter before migration took place. 4. All 55 species studied had earlier first flight trends at rate of β=‐0.611 ±se 0.015 days year‐1. Of these species, 49% had earlier last flights but the average species effect appeared relatively stationary (β=‐0.010 ±se 0.022 days year‐1). Most species (85%) showed increasing duration of their flight season (β=0.336 ±se 0.026 days year‐1), even though only 54% increased their annual count (β=0.002 ±se
       
  • Forecasting spring from afar' Timing of migration and predictability
           of phenology along different migration routes of an avian herbivore
    • Abstract: 1.Herbivorous birds are hypothesized to migrate in spring along a seasonal gradient of plant profitability towards their breeding grounds (green wave hypothesis). For Arctic‐breeding species in particular, following highly profitable food is important, so that they can replenish resources along the way and arrive in optimal body condition to start breeding early. 2.We compared the timing of migratory movements of Arctic‐breeding geese on different flyways to examine whether flyways differed in the predictability of spring conditions at stopovers, and whether this was reflected in the degree to which birds were following the green wave. 3.Barnacle geese (Branta leucopsis) were tracked with solar Argos/GPS PTTs from their wintering grounds to breeding sites in Greenland (N = 7), Svalbard (N = 21) and the Barents Sea (N = 12). The numerous stopover sites of all birds were combined into a set of 16 general stopover regions. 4.The predictability of climatic conditions along the flyways was calculated as the correlation and slope between onsets of spring at consecutive stopovers. These values differed between sites, mainly because of the presence or absence of ecological barriers. Goose arrival at stopovers was more closely tied to the local onset of spring when predictability was higher and when geese attempted breeding that year. 5.All birds arrived at early stopovers after the onset of spring and arrived at the breeding grounds before the onset of spring, thus overtaking the green wave. This is in accordance with patterns expected for capital breeders: first they must come into condition; at intermediate stopovers arrival with the food quality peak is important to stay in condition and at the breeding grounds early arrival is favoured so that hatching of young can coincide with the peak of food quality. 6.Our results suggest that a chain of correlations between climatic conditions at subsequent stopovers enables geese to closely track the green wave. However, the birds’ precision of migratory timing seems uninfluenced by ecological barriers, indicating partly fixed migration schedules. These might become non‐optimal due to climate warming and preclude accurate timing of long‐distance migrants in the future. This article is protected by copyright. All rights reserved.
       
  • Predator‐dependent functional response in wolves: From food
           limitation to surplus killing
    • Abstract: The functional response of a predator describes the change in per capita kill rate to changes in prey density. This response can be influenced by predator densities, giving a predator‐dependent functional response. In social carnivores which defend a territory, kill rates also depend on the individual energetic requirements of group members and their contribution to the kill rate. This study aims to provide empirical data for the functional response of wolves Canis lupus to the highly managed moose Alces alces population in Scandinavia. We explored prey and predator dependence, and how the functional response relates to the energetic requirements of wolf packs. Winter kill rates of GPS‐collared wolves and densities of cervids were estimated for a total of 22 study periods in 15 wolf territories. The adult wolves were identified as the individuals responsible for providing kills to the wolf pack, while pups could be described as inept hunters. The predator‐dependent, asymptotic functional response models (i.e. Hassell‐Varley type II and Crowley‐Martin) performed best among a set of 23 competing linear, asymptotic and sigmoid models. Small wolf packs acquired > 3 times as much moose biomass as required to sustain their field metabolic rate (FMR), even at relatively low moose abundances. Large packs (6 ‐ 9 wolves) acquired less biomass than required in territories with low moose abundance. We suggest the surplus‐killing by small packs is a result of an optimal foraging strategy to consume only the most nutritious parts of easy accessible prey while avoiding the risk of being detected by humans. Food limitation may have a stabilizing effect on pack size in wolves, as supported by the observed negative relationship between body weight of pups and pack size. This article is protected by copyright. All rights reserved.
       
  • Predators, energetics and fitness drive neonatal reproductive failure in
           red squirrels
    • Abstract: Neonatal reproductive failure should occur when energetic costs of parental investment outweigh fitness benefits. However, little is known about the drivers of neonatal reproductive failure in free ranging species experiencing continuous natural variation in predator abundance and in the energetic and fitness costs and benefits associated with parental investment. Long‐term comprehensive studies are required to better understand how biotic, abiotic, and life history conditions interact to drive occurrences of reproductive failure in the wild. Using 24 years (1987‐2011) of reproductive data from a northern boreal population of North American red squirrels in southwestern Yukon, we examined the effects of predator abundance, energetics (resource availability, ambient temperature and litter size), and fitness benefits (probability of overwinter juvenile survival and maternal age) on occurrences of neonatal reproductive failure (494/2670 reproductive attempts; 18.5%). Neonatal reproductive failure was driven by a combination of predator abundance, and the energetic and fitness costs and benefits of parental investment. The abundance of mustelids and maternal age were positively related to the occurrence of neonatal reproductive failure. High energy costs associated with a combination of low resource availability and cold ambient temperatures or large litters, corresponded to increased occurrences of neonatal reproductive failure. However, the strength of these relationships was influenced by variation in juvenile overwinter survival (i.e. fitness benefits). We provide evidence that predation pressure is an important driver of neonatal reproductive failure. In addition, we found a trade‐off occurs between resource‐dependent energetic and fitness costs and benefits of raising the current litter to independence. This article is protected by copyright. All rights reserved.
       
  • Effects of land‐use intensity on arthropod species abundance
           distributions in grasslands
    • Abstract: 1.As a rule, communities consist of few abundant and many rare species, which is reflected in the characteristic shape of species abundance distributions (SADs). The processes that shape these SADs have been a longstanding problem for ecological research. Although many studies found strong negative effects of increasing land‐use intensity on diversity, few reports consider land‐use effects on SADs. 2.Arthropods (insects and spiders) were sampled on 142 grassland plots in three regions in Germany, which were managed with different modes (mowing, fertilisation and/or grazing) and intensities of land use. We analysed the effect of land use on three parameters characterizing the shape of SADs: abundance decay rate (the steepness of the rank abundance curve, represented by the niche‐preemption model parameter), dominance (Berger‐Parker dominance) and rarity (Fisher's alpha). Furthermore, we tested the core‐satellite hypothesis by comparing the species’ rank within the SAD to their distribution over the land‐use gradient. 3.When data on Araneae, Cicadina, Coleoptera, Heteroptera and Orthoptera were combined, abundance decay rate increased with combined land‐use intensity (including all modes). Among the single land‐use modes, increasing fertilisation and grazing intensity increased the decay rate of all taxa while increasing mowing frequency significantly affected the decay rate only in interaction with fertilisation. Results of single taxa differed in their details, but all significant interaction effects included fertilisation intensity. Dominance generally increased with increasing fertilisation and rarity decreased with increasing grazing or mowing intensity, despite small differences among taxa and regions. The majority of species found on less than 10% of the plots per region were generally rare (
       
  • Ecological Implications of Reduced Forage Quality on Growth and Survival
           of Sympatric Geese
    • Abstract: 1.Allometric constraints associated with digesting leaves require relatively small avian herbivores to consume high‐quality forage. How such constraints are overcome during ontogeny when energy and nutrient requirements are relatively high has not been adequately explored. 2.We compared growth trajectories of Canada and lesser snow goose goslings raised on grass‐based diets that differed in protein (10, 14, or 18%) and fiber (30 or 45%) with those of free‐living goslings on Akimiski Island, Canada. This common‐garden experiment allowed us to test the hypotheses that (1) smaller‐bodied geese are more negatively affected by reduced forage quality than larger‐bodied geese, and (2) goslings from subarctic brood‐rearing areas have a limited capacity to slow growth in response to reduced forage quality. 3.Canada goose goslings fed low protein (10%) diets were on average 44% lighter in body mass, had slower growth rates, and were delayed >20 days in reaching 90% of asymptotic size compared to Canada goose goslings fed 18% protein. In contrast, snow goose goslings were unable to survive on the low protein diets, and those fed high or medium protein diets grew at a similar rate and achieved similar asymptotic size. Canada and snow goose goslings fed low protein diets had reduced growth rates of the tarsus and delayed emergence of the 9th primary. 4.Free‐ranging Canada goslings on Akimiski Island were similar in mass and structural size to captive‐reared goslings fed low protein diets. In contrast, snow goslings were similar in mass and structural size to the captive‐reared goslings fed the high and medium protein diets. This suggests that degraded habitats with mostly low protein forage may be able to support Canada goslings better than snow goslings which require higher quality forage to survive. 5.Size‐related differences in gosling growth and survival in response to diminished diet quality may influence population size when available food reaches a lower threshold in protein content. However, goslings can avoid such density‐dependent population regulation if they are able to move their broods and find adequate quality and quantity of forage. This article is protected by copyright. All rights reserved.
       
  • How Ebola impacts social dynamics in gorillas: a multistate modelling
           approach
    • Abstract: Emerging infectious diseases can induce rapid changes in population dynamics and threaten population persistence. In socially structured populations, the transfers of individuals between social units, for example, from breeding groups to non‐breeding groups, shape population dynamics. We suggest that diseases may affect these crucial transfers. We aimed to determine how disturbance by an emerging disease affects demographic rates of gorillas, especially transfer rates within populations and immigration rates into populations. We compared social dynamics and key demographic parameters in a gorilla population affected by Ebola using a long‐term observation data set including pre‐, during and post‐outbreak periods. We also studied a population of undetermined epidemiological status in order to assess whether this population was affected by the disease. We developed a multistate model that can handle transition between social units while optimizing the number of states. During the Ebola outbreak, social dynamics displayed increased transfers from a breeding to a non‐breeding status for both males and females. Six years after the outbreak, demographic and most of social dynamics parameters had returned to their initial rates, suggesting a certain resilience in the response to disruption. The formation of breeding groups increased just after Ebola, indicating that environmental conditions were still attractive. However, population recovery was likely delayed because compensatory immigration was probably impeded by the potential impact of Ebola in the surrounding areas. The population of undetermined epidemiological status behaved similarly to the other population before Ebola. Our results highlight the need to integrate social dynamics in host‐population demographic models to better understand the role of social structure in the sensitivity and the response to disease disturbances. The authors provide a general framework for studying social dynamics in disturbed contexts and apply it to the case of a gorilla population affected by Ebola.
       
  • Territoriality and home‐range dynamics in meerkats, Suricata
           suricatta: a mechanistic modelling approach
    • Abstract: Multiple approaches exist to model patterns of space use across species, among them resource selection analysis, statistical home range modelling, and mechanistic movement modelling. Mechanistic home‐range models combine the benefits of these approaches, describing emergent territorial patterns based on fine‐scale individual‐ or group‐movement rules and incorporating interactions with neighbours and the environment. These models have not, to date, been extended to dynamic contexts. Using mechanistic home‐range models, we explore meerkat (Suricata suricatta) territorial patterns, considering scent marking, direct group interactions, and habitat selection. We also extend the models to accommodate dynamic aspects of meerkat territoriality (territory development and territory shift). We fit models, representing multiple working hypotheses, to data from a long‐term meerkat study in South Africa, and we compare models using Akaike's and Bayesian information criteria. Our results identify important features of meerkat territorial patterns. Notably, larger groups do not seem to control larger territories, and groups apparently prefer dune edges along a dry riverbed. Our model extensions capture instances in which 1) a newly formed group interacts more strongly with its parent groups over time and 2) a group moves its territory core out of aversive habitat. This extends our mechanistic modelling framework in previously unexplored directions. This article is protected by copyright. All rights reserved.
       
  • Habitat‐based polymorphism is common in stream fishes
    • Abstract: 1. Morphological differences (size and shape) across habitats are common in lake fish where differences relate to two dominant contrasting habitats: the pelagic and littoral habitat. Repeated occurrence of littoral and pelagic morphs across multiple populations of several lake fish species has been considered as important evidence that polymorphism is adaptive in these systems. It has been suggested that these habitat‐based polymorphic differences are due to the temporal stability of the differences between littoral and pelagic habitats. 2. Although streams are spatially heterogeneous, they are also more temporally dynamic than lakes and it is still an open question whether streams provide the environmental conditions that promote habitat‐based polymorphism. We tested whether fish from riffle, run and pool habitats, respectively, differed consistently in their morphology. 3. Our test compared patterns of morphological variation (size and shape) in 10 fish species from the three stream habitat types in 36 separate streams distributed across three watersheds. 4. For most species, body size and shape (after controlling for body size) differed across riffle, run and pool habitats. Unlike many lake species, the nature of these differences was not consistent across species, possibly because these species use these habitat types in different ways. 5. Our results suggest that habitat‐based polymorphism is an important feature also in stream‐fishes despite the fact that streams are temporally variable in contrast to lake systems. Future research is required to assess whether the patterns of habitat‐polymorphism encountered in streams have a genetic basis or they are simply the result of within generation phenotypic plasticity. This article is protected by copyright. All rights reserved.
       
  • Impacts of breeder loss on social structure, reproduction and population
           growth in a social canid
    • Abstract: The importance of individuals to the dynamics of populations may depend on reproductive status, especially for species with complex social structure. Loss of reproductive individuals in socially complex species could disproportionately affect population dynamics by destabilizing social structure and reducing population growth. Alternatively, compensatory mechanisms such as rapid replacement of breeders may result in little disruption. The impact of breeder loss on the population dynamics of social species remains poorly understood. We evaluated the effect of breeder loss on social stability, recruitment and population growth of grey wolves (Canis lupus) in Denali National Park and Preserve, Alaska using a 26‐year dataset of 387 radiocollared wolves. Harvest of breeding wolves is a highly contentious conservation and management issue worldwide, with unknown population‐level consequences. Breeder loss preceded 77% of cases (n = 53) of pack dissolution from 1986 to 2012. Packs were more likely to dissolve if a female or both breeders were lost and pack size was small. Harvest of breeders increased the probability of pack dissolution, likely because the timing of harvest coincided with the breeding season of wolves. Rates of denning and successful recruitment were uniformly high for packs that did not experience breeder loss; however, packs that lost breeders exhibited lower denning and recruitment rates. Breeder mortality and pack dissolution had no significant effects on immediate or longer term population dynamics. Our results indicate the importance of breeding individuals is context dependent. The impact of breeder loss on social group persistence, reproduction and population growth may be greatest when average group sizes are small and mortality occurs during the breeding season. This study highlights the importance of reproductive individuals in maintaining group cohesion in social species, but at the population level socially complex species may be resilient to disruption and harvest through strong compensatory mechanisms. This paper quantitatively evaluates how the death of reproductive individuals in socially complex canid species could affect social group cohesion and population growth.
       
  • Ecological causes of multilevel covariance between size and
           first‐year survival in a wild bird population
    • Abstract: Estimates of selection in natural populations are frequent but our understanding of ecological causes of selection, and causes of variation in the direction, strength and form of selection is limited. Here, we apply a multilevel framework to partition effects of great tit fledging mass on first‐year survival to hierarchical levels and quantify their ecological dependence using a data set spanning 51 years. We show that estimates of the effect of fledging mass on first‐year survival decline threefold from year‐ to brood‐ to individual level, so that estimates of selection depend strongly on the level at which they are calculated. We identify variables related to summer and winter food availability as underlying higher‐level effects of fledging mass on first‐year survival and show experimentally that brood‐level effects originate early in development. Further, we show that predation and conspecific density modulate individual‐level effects of fledging mass on first‐year survival. These analyses demonstrate how correlations between traits, fitness and environment influence estimates of selection and show how partitioning trait effects between levels of selection and environmental factors is a promising approach to identify potential agents of selection. The paper demonstrates how correlations between traits, fitness and environment influence estimates of selection, and shows how partitioning trait‐effects between levels of selection and environmental factors is a promising approach to identify potential agents of selection.
       
  • Experimental manipulation of female reproduction demonstrates its fitness
           costs in kangaroos
    • Abstract: When resources are scarce, female mammals should face a trade‐off between lactation and other life‐history traits such as growth, survival and subsequent reproduction. Kangaroos are ideal to test predictions about reproductive costs because they may simultaneously lactate and carry a young, and have indeterminate growth and a long breeding season. An earlier study in three of our five study populations prevented female eastern grey kangaroos (Macropus giganteus) from reproducing during one reproductive season by either inserting contraceptive implants or removing very small pouch young. We explored how individual and environmental variables affect the costs of reproduction over time, combining this experimental reduction of reproductive effort with multi‐year monitoring of 270 marked females. Experimental manipulation should control for individual heterogeneity, revealing the costs of reproduction and their likely sources. We also examined the fitness consequences of reproductive effort and offspring sex among unmanipulated individuals to test whether sex allocation strategies affected trade‐offs. Costs of reproduction included longer inter‐birth intervals and lower probability of producing a young that survived to 7 months in the subsequent reproductive event. Weaning success, however, did not differ significantly between manipulated and control females. By reducing reproductive effort, manipulation appeared to increase individual condition and subsequent reproductive success. Effects of offspring sex upon subsequent reproductive success varied according to year and study population. Mothers of sons were generally more likely to have a young that survived to 7 months, compared to mothers of daughters. The fitness costs of reproduction arise from constraints in both acquisition and allocation of resources. To meet these costs, females delay subsequent parturition and may manipulate offspring sex. Reproductive tactics thus vary according to the amount of resource available to each individual, promoting a wide range in reproductive performance within and among individuals and populations. By combining the first experimental manipulation of reproductive effort in wild marsupials with long‐term monitoring of multiple populations, the authors quantify the fitness consequences of reproduction.
       
  • Individual and species specific traits explain niche size and functional
           role in spiders as generalist predators
    • Abstract: 1. The function of a predator within a community is greatly based on its trophic niche, i.e. the number and the strength of feeding links. In generalist predators, which feed on a wide range of prey, the size and position of the trophic niche is likely determined by traits such as hunting mode, the stratum they occur in, their body size and age. 2. We used stable isotope analyses (13C and 15N) to measure the trophic niche size of nine spider species within a forest hedge community and tested for species traits and individual traits that influence stable isotope enrichment, niche size, and resource use. 3. The spiders Enoplognatha, Philodromus, Floronia, and Heliophanus had large isotopic niches, which correspond to a more generalistic feeding behaviour. In contrast, Araneus, Metellina, and Agelena, as top predators in the system, had rather narrow niches. We found a negative correlation between trophic position and niche size. Differences in trophic position in spiders were explained by body size, hunting modes and stratum, while niche size was influenced by hunting mode. In Philodromus the size of the trophic niche increased significantly with age. 4. Fitting spiders to functional groups according to their mean body size, hunting mode and their habitat domain resulted in largely separated niches, which indicates that these traits are meaningful for separating functional entities in spiders. Functional groups based on habitat domain (stratum) caught the essential functional differences between the species with species higher up in the vegetation feeding on flying insects and herb and ground species also preying on forest floor decomposers. 5. Interestingly, we found a gradient from large species using a higher habitat domain and having a smaller niche to smaller species foraging closer to the ground and having a larger niche. This shows that even within generalist predators, such as spiders, there is a gradient of specialism that can be predicted by functional traits. This article is protected by copyright. All rights reserved.
       
  • How topography induces reproductive asynchrony and alters gypsy moth
           invasion dynamics
    • Abstract: 1. Reproductive asynchrony, a temporal mismatch in reproductive maturation between an individual and potential mates, may contribute to mate‐finding failure and Allee effects that influence the establishment and spread of invasive species. Variation in elevation is likely to promote variability in maturation times for species with temperature‐dependent development, but it is not known how strongly this influences reproductive asynchrony or the population growth of invasive species. 2. We examined whether spatial variation in reproductive asynchrony, due to differences in elevation and local heterogeneity in elevation (hilliness), can explain spatial heterogeneity in the population growth rate of the gypsy moth, Lymantria dispar (L.), along its invasion front in Virginia and West Virginia, USA. 3. We used a spatially explicit model of the effects of reproductive asynchrony on mating success to develop predictions of the influences of elevation and elevational heterogeneity on local population growth rates. Population growth rates declined with increased elevation and more modestly with increased elevational heterogeneity. As in earlier work, we found a positive relationship between the population growth rate and the number of introduced egg masses, indicating a demographic Allee effect. At high elevations and high heterogeneity in elevation, the population growth rate was lowest and the density at which the population tended to replace itself (i.e., the Allee threshold) was highest. 4. An analysis of 22 years of field data also showed decreases in population growth rates with elevation and heterogeneity in elevation that were largely consistent with the model predictions. 5. These results highlight how topographic characteristics can affect reproductive asynchrony and influence mate‐finding Allee effects in an invading non‐native insect population. Given the dependence of developmental rates on temperature in poikilotherms, topographic effects on reproductive success could potentially be important to the population dynamics of many organisms. This article is protected by copyright. All rights reserved.
       
  • Empirical tests of harvest‐induced body‐size evolution along a
           geographic gradient in Australian macropods
    • Abstract: 1.Life‐history theory predicts the progressive dwarfing of animal populations that are subjected to chronic mortality stress but the evolutionary impact of harvesting terrestrial herbivores has seldom been tested. In Australia, marsupials of the genus Macropus (kangaroos and wallabies) are subjected to size‐selective commercial harvesting. Mathematical modelling suggests that harvest quotas (ca. 10–20% of population estimates annually) could be driving body‐size evolution in these species. 2.We tested this hypothesis for three harvested macropod species with continental‐scale distributions. To do so, we measured more than 2 000 macropod skulls sourced from wildlife collections spanning the last 130 years. We analysed these data using spatial Bayesian models that controlled for the age and sex of specimens as well as environmental drivers and island effects. 3.We found no evidence for the hypothesized decline in body size for any species; rather, models that fit trend terms supported minor body size increases over time. This apparently counterintuitive result is consistent with reduced mortality due to a depauperate predator guild and increased primary productivity of grassland vegetation following European settlement in Australia. 4.Spatial patterns in macropod body size supported the heat dissipation limit and productivity hypotheses proposed to explain geographic body‐size variation (i.e., skull size increased with decreasing summer maximum temperature and increasing rainfall, respectively). 5.There is no empirical evidence that size‐selective harvesting has driven the evolution of smaller body size in Australian macropods. Bayesian models are appropriate for investigating the long‐term impact of human harvesting because they can impute missing data, fit non‐linear growth models and account for non‐random spatial sampling inherent in wildlife collections. This article is protected by copyright. All rights reserved.
       
  • How detectable is predation in stage‐structured populations'
           Insights from a simulation‐testing analysis
    • Abstract: The potential of predation to structure marine food webs is widely acknowledged. However, available tools to detect the regulation of prey population dynamics by predation are limited, partly because available population data often aggregate a population's age structure into a single biomass or abundance metric. Additionally, many food webs are relatively complex, with prey species subject to different assemblages of predators throughout their ontogeny. The goal of this study was to evaluate the extent to which stage‐structured predation could be reliably detected from time series of total biomass of predators and prey. We simulated age‐structured populations of four mid‐trophic level fish species with distinct life history traits, exposed them to variable predation at different life stages, and fit production models to resulting population biomass to determine how reliably the effects of predators could be detected. Predation targeting early life history and juvenile life stages generally led to larger fluctuations in annual production, and was therefore more detectable. However, ecologically‐realistic levels of observation error and environmental stochasticity masked most predator signals. The addition of predation at a second life stage sharply decreased the ability to detect the effect of each predator. We conclude an absence of detectable species interactions from biomass time series may be partly due to the interactive effects of environmental variability and complex food web linkages and life histories. We also note that predation signals are most robust for predator‐prey systems where predators primarily act on mortality of sub‐mature life history stages. Simulation testing can be applied widely to evaluate the statistical power of analyses to detect predation effects. This article is protected by copyright. All rights reserved.
       
  • “You shall not pass!”: quantifying barrier permeability and
           proximity avoidance by animals
    • Abstract: 1. Impediments to animal movement are ubiquitous and vary widely in both scale and permeability. It is essential to understand how impediments alter ecological dynamics via their influence on animal behavioural strategies governing space use and, for anthropogenic features such as roads and fences, how to mitigate these effects to effectively manage species and landscapes. 2. Here, we focused primarily on barriers to movement, which we define as features that cannot be circumnavigated but may be crossed. Responses to barriers will be influenced by the movement capabilities of the animal, its proximity to the barriers, and habitat preference. We developed a mechanistic modelling framework for simultaneously quantifying the permeability and proximity effects of barriers on habitat preference and movement. 3. We used simulations based on our model to demonstrate how parameters on movement, habitat preference and barrier permeability can be estimated statistically. We then applied the model to a case study of road effects on wild mountain reindeer summer movements. 4. This framework provided unbiased and precise parameter estimates across a range of strengths of preferences and barrier permeabilities. The quality of permeability estimates, however, was correlated with the number of times the barrier is crossed and the number of locations in proximity to barriers. In the case study we found reindeer avoided areas near roads and that roads are semi‐permeable barriers to movement. There was strong avoidance of roads extending up to approximately 1 km for four of five animals, and having to cross roads reduced the probability of movement by 68.6% (range 3.5‐99.5%). 5. Human infrastructure has embedded within it the idea of networks: nodes connected by linear features such as roads, rail tracks, pipelines, fences and cables, many of which divide the landscape and limit animal movement. The unintended but potentially profound consequences of infrastructure on animals remain poorly understood. The rigorous framework for simultaneously quantifying movement, habitat preference and barrier permeability developed here begins to address this knowledge gap. This article is protected by copyright. All rights reserved.
       
  • Movement propensity and ability correlate with ecological specialisation
           in European land snails: comparative analysis of a dispersal syndrome
    • Abstract: Intra‐ and inter‐specific differences in movement behaviour play an important role in the ecology and evolution of animals, particularly in fragmented landscapes. As a consequence of rarer and generally more fragmented habitat, and because dispersal tends to disrupt benefits brought by local adaptation, theory predicts that mobility and dispersal should be counter‐selected in specialists. Using experimental data and phylogenetic comparative tools, we analysed movement propensity and capacity, as well as dispersal‐related phenotypic traits, in controlled conditions in 20 species of European land snails from the Helicoidea superfamily. Costs of movement in terrestrial gastropods are among the highest in animals, which make them a potentially powerful model to test these predictions. Habitat specialists were indeed less likely to cross a boundary between a familiar and an unfamiliar substrate than generalists. They also had smaller feet, after accounting for size. Furthermore, exploring specialists were slower than generalists, and had more tortuous trajectories, leading them to stay closer to the familiar patch. Movement traits were generally evolutionary labile, but some were constrained by body size, a phylogenetically conserved trait. High specialisation and low dispersal ability are two traits often considered to increase species vulnerability to fragmentation, climate changes and extinction. This study confirms they should not be considered separately, due to their integration in a dispersal syndrome. Therefore, specialist species face double penalty under habitat loss and other environmental changes, making them more vulnerable to extinction and contributing to the biotic homogenization of communities. This article is protected by copyright. All rights reserved.
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2014