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ENVIRONMENTAL STUDIES (704 journals)            First | 1 2 3 4 5 6 7 8     

Marine Ecology     Hybrid Journal   (Followers: 13)
Marine Environmental Research     Hybrid Journal   (Followers: 12)
Marine Pollution Bulletin     Hybrid Journal   (Followers: 11)
Materials for Renewable and Sustainable Energy     Open Access   (Followers: 7)
Mathematical and Computational Forestry & Natural-Resource Sciences     Free  
Mathematical Population Studies: An International Journal of Mathematical Demography     Hybrid Journal   (Followers: 2)
Medio Ambiente y Urbanizacion     Full-text available via subscription  
Membranes     Open Access   (Followers: 4)
Michigan Journal of Sustainability     Open Access  
Midwest Studies In Philosophy     Hybrid Journal   (Followers: 10)
Mine Water and the Environment     Hybrid Journal   (Followers: 6)
Mitigation and Adaptation Strategies for Global Change     Hybrid Journal   (Followers: 12)
Modern Asian Studies     Hybrid Journal   (Followers: 5)
Modern Cartography Series     Full-text available via subscription   (Followers: 6)
Mountain Research and Development     Open Access   (Followers: 3)
Multequina     Open Access  
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis     Hybrid Journal   (Followers: 2)
Mutation Research/Genetic Toxicology and Environmental Mutagenesis     Hybrid Journal   (Followers: 8)
Nativa     Open Access  
Natur und Recht     Hybrid Journal   (Followers: 6)
Natural Areas Journal     Full-text available via subscription   (Followers: 7)
Natural Hazards     Hybrid Journal   (Followers: 214)
Natural Resources     Open Access  
Natural Resources and Environmental Issues     Open Access   (Followers: 5)
Nature and Culture     Full-text available via subscription   (Followers: 9)
NeuroToxicology     Hybrid Journal   (Followers: 1)
Neurotoxicology and Teratology     Hybrid Journal   (Followers: 2)
NEW SOLUTIONS: A Journal of Environmental and Occupational Health Policy     Full-text available via subscription   (Followers: 6)
New Zealand Journal of Environmental Law     Full-text available via subscription   (Followers: 3)
NJAS - Wageningen Journal of Life Sciences     Full-text available via subscription   (Followers: 1)
Noise Notes     Full-text available via subscription   (Followers: 3)
Novos Cadernos NAEA     Open Access  
Observatorio Medioambiental     Open Access  
Occupational and Environmental Medicine     Full-text available via subscription   (Followers: 8)
Ocean Acidification     Open Access  
Oecologia     Hybrid Journal   (Followers: 25)
Oikos     Hybrid Journal   (Followers: 31)
Open Journal of Ecology     Open Access   (Followers: 10)
Open Journal of Marine Science     Open Access   (Followers: 6)
Open Journal of Modern Hydrology     Open Access   (Followers: 1)
Our Nature     Open Access   (Followers: 2)
Oxford Journal of Legal Studies     Hybrid Journal   (Followers: 16)
Pace Environmental Law Review     Open Access   (Followers: 4)
Palaeobiodiversity and Palaeoenvironments     Hybrid Journal   (Followers: 3)
Papers on Global Change IGBP     Open Access   (Followers: 1)
Particle and Fibre Toxicology     Open Access   (Followers: 3)
Pastos y Forrajes     Open Access  
Pesquisa em Educação Ambiental     Open Access  
Pharmacology & Therapeutics     Hybrid Journal   (Followers: 5)
Pharmacology Biochemistry and Behavior     Hybrid Journal   (Followers: 1)
Philosophical Studies     Hybrid Journal   (Followers: 8)
Physio-Géo     Open Access   (Followers: 2)
Pittsburgh Journal of Environmental and Public Health Law     Open Access   (Followers: 1)
Planet     Open Access   (Followers: 1)
Planning & Environmental Law: Issues and decisions that impact the built and natural environments     Hybrid Journal   (Followers: 6)
Plant Ecology & Diversity     Partially Free   (Followers: 11)
Plant Knowledge Journal     Open Access   (Followers: 2)
Plant, Cell & Environment     Hybrid Journal   (Followers: 4)
Polar Journal     Hybrid Journal   (Followers: 1)
Policy Studies     Hybrid Journal   (Followers: 7)
Policy Studies Journal     Hybrid Journal   (Followers: 5)
Polish Polar Research     Open Access   (Followers: 4)
Political Studies     Hybrid Journal   (Followers: 22)
Political Studies Review     Hybrid Journal   (Followers: 14)
Population and Environment     Hybrid Journal   (Followers: 6)
Population Ecology     Hybrid Journal   (Followers: 9)
Population Studies: A Journal of Demography     Hybrid Journal   (Followers: 6)
Postcolonial Studies     Hybrid Journal   (Followers: 6)
Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management     Full-text available via subscription   (Followers: 3)
Presence Teleoperators & Virtual Environments     Hybrid Journal   (Followers: 1)
Presidential Studies Quarterly     Hybrid Journal   (Followers: 4)
Procedia Environmental Sciences     Open Access   (Followers: 2)
Proceedings of ICE, Waste and Resource Management     Hybrid Journal   (Followers: 3)
Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment     Hybrid Journal   (Followers: 1)
Proceedings of the International Academy of Ecology and Environmental Sciences     Open Access   (Followers: 4)
Process Safety and Environmental Protection     Hybrid Journal   (Followers: 3)
Progress in Industrial Ecology, An International Journal     Hybrid Journal   (Followers: 4)
Psychological Assessment     Full-text available via subscription   (Followers: 5)
Public Money & Management     Hybrid Journal   (Followers: 4)
Public Works Management & Policy     Hybrid Journal   (Followers: 5)
Qatar Foundation Annual Research Forum Proceedings     Open Access   (Followers: 3)
Radioactivity in the Environment     Full-text available via subscription   (Followers: 4)
Regional Environmental Change     Hybrid Journal   (Followers: 3)
Regional Studies     Hybrid Journal   (Followers: 6)
Religious Studies     Hybrid Journal   (Followers: 11)
RELP - Renewable Energy Law and Policy     Full-text available via subscription   (Followers: 4)
Remediation Journal     Hybrid Journal   (Followers: 5)
Remote Sensing Letters     Hybrid Journal   (Followers: 9)
Renaissance Studies     Hybrid Journal   (Followers: 13)
Rendiconti Lincei     Hybrid Journal  
Renewable Energy Focus     Full-text available via subscription   (Followers: 7)
Research & Reviews : Journal of Ecology     Full-text available via subscription  
Research and Practice for Persons with Severe Disabilities     Full-text available via subscription   (Followers: 4)
Research Journal of Environmental Sciences     Open Access   (Followers: 1)
Research Journal of Environmental Toxicology     Open Access   (Followers: 2)
ReSource     Full-text available via subscription  
Resources     Open Access  
Resources, Conservation and Recycling     Hybrid Journal   (Followers: 9)
Reuse/Recycle Newsletter     Hybrid Journal   (Followers: 1)
Review of English Studies     Hybrid Journal   (Followers: 7)

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Journal Cover Theoretical Ecology
   Journal TOC RSS feeds Export to Zotero [11 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1874-1746 - ISSN (Online) 1874-1738
     Published by Springer-Verlag Homepage  [2209 journals]   [SJR: 1.37]   [H-I: 10]
  • A stochastic biodiversity model with overlapping niche structure
    • Abstract: Abstract The niche is a fundamental ecological concept that underpins many explanations of patterns of biodiversity. The complexity of niche processes in ecological systems, however, means that it is difficult to capture them accurately in theoretical models of community assembly. In this study, we build upon simple neutral biodiversity models by adding the important ingredient of overlapping niche structure. Our model is spatially implicit and contains a fixed number of equal-sized habitats. Each species in the metacommunity arises through a speciation event; at which time, it is randomly assigned a fundamental niche or set of environments/habitats in which it can persist. Within each habitat, species compete with other species that have different but overlapping fundamental niches. Species abundances then change through ecological drift; each, however, is constrained by its maximum niche breadth and by the presence of other species in its habitats. Using our model, we derive analytical expressions for steady-state species abundance distributions, steady-state distributions of niche breadth across individuals and across species, and dynamic distributions of niche breadth across species. With this framework, we identify the conditions that produce the log-series species abundance distribution familiar from neutral models. We then identify how overlapping niche structure can lead to other species abundance distributions and, in particular, ask whether these new distributions differ significantly from species abundance distributions predicted by non-overlapping niche models. Finally, we extend our analysis to consider additional distributions associated with realized niche breadths. Overall, our results show that models with overlapping niches can exhibit behavior similar to neutral models, with the caveat that species with narrow fundamental niche breadths will be very rare. If narrow-niche species are common, it must be because they are in a non-overlapping niche or have countervailing advantages over broad-niche species. This result highlights the role that niches can play in establishing demographic neutrality.
      PubDate: 2014-09-20
  • Modeling the dynamics of soil erosion and vegetative control —
           catastrophe and hysteresis
    • Abstract: Abstract Wildfire events and anthropogenic activities such as agriculture and livestock grazing may denude the landscape from vegetation cover, resulting in systems prone to soil loss and degradation. Soil dynamics is an intricate process balanced between pedogenesis, which is a relatively slow process, and erosion which depends on many inert (e.g., soil texture, slope, precipitation, and wind) and biological factors such as vegetation properties, grazing intensity, and human disturbance. We develop here a theoretical model of the global dynamics of the interactions between vegetation and soil. Assuming a double feedback between them—plants control erosion, and soil availability facilitates plants growth—a system of nonlinear differential equations is derived, and the outcomes are investigated. The range of realistic parameter values were taken from the literature. Complex properties emerge from this model. For some ranges of parameter values, the model predicts one of two types of steady states—full recovery of vegetation cover or a degraded barren system. For another range of parameter values, bistability appears. We identify the parameter combinations which determine the qualitative behavior of the system and the threshold values beyond which the system becomes bistable. The model predicts that certain ecosystems are highly stable. Others might be bistable transitioning between these two states through perturbations. Therefore, the possibly of hysteresis as parameters vary arises, as well as the ability of the system to shift between steady states, possibly leading to sudden and dramatic changes.
      PubDate: 2014-09-11
  • Heterogeneity in symbiotic effects facilitates        class="a-plus-plus">Wolbachia establishment in
           insect populations
    • Abstract: Abstract Facultative vertically transmitted bacterial symbionts often manipulate its host’s reproductive biology and thus facilitate their persistence. Wolbachia is one such symbiont where frequency-dependent reproductive benefits are opposed by frequency-independent fitness costs leading to bistable dynamics. Introduction of carriers does not assure invasion unless the initial frequency is above a threshold determined by the balance of costs and benefits. Recent laboratory experiments have uncovered that Wolbachia also protects their hosts from pathogens. The expected consequence of this phenotype in natural environments is to lower the invasion threshold by a factor that increases with the extent of pathogen exposure. Here, we introduce a series of mathematical models to address how pathogen protection affects Wolbachia invasion. First, under homogeneous symbiotic effects, we obtain an analytical expression for the invasion threshold in terms of pathogen exposure, and find a regime where symbiont releases may result in elimination of the entire host population provided that abundance of virulent pathogens is high. Second, we distribute Wolbachia effects such that some carriers are totally protected and others not at all, and explore how this interplays with different pathogen intensities, to conclude that heterogeneity further lowers the threshold for Wolbachia invasion. Third, we replicate the analysis using a realistic distribution of protective effects and confirm that heterogeneity increases system resilience by reducing the odds of population collapse.
      PubDate: 2014-08-31
  • A two-strain ecoepidemic competition model
    • Abstract: Abstract In this paper, we consider a competition system in which two diseases spread by contact. We characterize the system behavior, establishing that only some configurations are possible. In particular, we discover that coexistence of the two strains is not possible, under the assumptions of the model. A number of transcritical bifurcations relates the more relevant system’s equilibria. Coexistence via persistent oscillations is shown. Bistability is shown between a situation in which only the disease-unaffected population thrives and another one containing only the second population with endemic disease. An accurate computation of the separating surface of the basins of attraction of these two mutually exclusive equilibria is obtained via novel results in approximation theory. The behavior of the ecosystem in some of the parameter spaces is investigated.
      PubDate: 2014-08-26
  • Role of trade-off between sexual and vertical routes for evolution of
           pathogen transmission
    • Abstract: Abstract Many pathogens that are predominantly sexually transmitted can also be transmitted vertically. On the other hand, nonbeneficial pathogens that are predominantly vertically transmitted appear to be rare to absent. Many infections also exist that are only transmitted sexually. Using an empirically suggested trade-off between the horizontal and vertical transmission modes, we develop and analyze a model to study evolutionary dynamics of sterilizing, sexually transmitted infections which can also be transmitted vertically. We assume several flexible forms of the trade-off and ask under which conditions evolution in nonbeneficial pathogens favors vertical transmission, sexual transmission, or a mixture of the two. The evolutionary analysis of our model reveals a rich spectrum of evolutionary outcomes. In particular, evolution of pure sexual, pure vertical, and mixed transmission is possible, in addition to a frequent occurrence of evolutionary suicide. These outcomes can also arise via evolutionary branching and be combined in several evolutionary bistability regimes. We show that the shape of the trade-off between the two transmission modes significantly affects pathogen evolution. In particular, while vertical transmission dominates for concave and sigmoid trade-offs, sexual transmission is most commonly observed under convex trade-offs. Our analysis can shed more light on when an infection adopts a particular evolutionary behavior, and which region of the parameter space is realistic, so something about the evolutionary process itself.
      PubDate: 2014-08-22
  • Effects of successive predator attacks on prey aggregations
    • Abstract: Abstract We study the cumulative effect of successive predator attacks on the disturbance of a prey aggregation using a modelling approach. Our model intends to represent fish schools attacked by both aerial and underwater predators. This individual-based model uses long-distance attraction and short-distance repulsion between prey, which leads to prey aggregation and swarming in the absence of predators. When intermediate-distance alignment is added to the model, the prey aggregation displays a cohesive displacement, i.e., schooling, instead of swarming. Including predators, i.e. with repulsion behaviour for prey to predators in the model, leads to flash expansion of the prey aggregation after a predator attack. When several predators attack successively, the prey aggregation dynamics is a succession of expanding-grouping-swarming/schooling phases. We quantify this dynamics by recording the changes in the simulated prey aggregation radius over time. This radius is computed as the longest distance of individual prey to the aggregation centroid, and it is assumed to increase along with prey disturbance. The prey aggregation radius generally increases during flash expansion, then decreases during grouping until reaching a constant lowest level during swarming/schooling. This general dynamics is modulated by several parameters: the frequency, direction (vertical vs. horizontal) and target (centroid of the prey aggregation vs. random prey) of predator attacks; the distance at which prey detect predators; the number of prey and predators. Our results suggest that both aerial and underwater predators are more efficient at disturbing fish schools by increasing their attack frequency at such level that the fish cannot return to swarming/schooling. We find that a mix between aerial and underwater predators is more efficient at disturbing a fish school than a single type of attack, suggesting that aerial and underwater foragers may gain mutual benefits in forming foraging groups.
      PubDate: 2014-08-01
  • Harmful algal blooms: combining excitability and competition
    • Abstract: Abstract Harmful algal blooms (HABs) characterized by a large concentration of toxic species appear rather rarely, but have a severe impact on the whole ecosystem. To study on possible trigger mechanisms for the emergence of HABs, we consider a nutrient-phytoplankton-zooplankton model to find the conditions under which a toxic phytoplankton species is able to form a bloom by winning the competition against its nontoxic competitor. The basic mechanism is related to the excitability of the system, i.e., the ability to develop a large response on certain perturbations. In a large class of models, a HAB results from a combined effect of nutrient enrichment and selective predation on different phytoplankton populations by zooplankton. We show that the severity of HAB is controlled by nutrient enrichment and zooplankton abundance, while the frequency of its occurrence depends on the strength of selectivity of predation. Thereby the intricate interplay between excitability, competition, and selective grazing pressure builds the backbone of the mechanism of the emergence of HABs.
      PubDate: 2014-08-01
  • Inferring topology from dynamics in spatial networks
    • Abstract: Abstract We examine the dynamics of oscillating populations in habitats described as networks of connected patches where the connections are not regular. This system would be typically analysed focusing either on the population dynamics, or measuring dispersal directly or indirectly. We focus on the question of the degree to which the dynamical patterns, as reflected in synchrony, reveal the underlying dispersal pathways. This would represent a bridge between two major spatial approaches: topological and dynamical. We show how local populations can be synchronized even if there is no direct dispersal route between them, while the stepping-stone populations are not synchronized. This leads to the surprising result that the topological structure of the underlying network is not reflected simply in patterns of synchrony across space in population dynamics. This shows that, with our current tools, the complex relationship between the underlying dispersal patterns and population dynamics prevent us from determining network structure through the observation of population dynamics.
      PubDate: 2014-07-31
  • A generalized perturbation approach for exploring stock recruitment
    • Abstract: Abstract Models of stock-recruitment relationships (SRRs) are often used to predict fish population dynamics. Commonly used SRRs include the Ricker, Beverton-Holt, and Cushing functional forms, which differ primarily by the degree of density-dependent effects (compensation). The degree of compensation determines whether recruitment respectively decreases, saturates, or increases at high levels of spawning stock biomass. In 1982, J.G. Shepherd united these dynamics into a single model, where the degree of compensation is determined by a single parameter. However, the difficulty in relating this parameter to biological data has limited its usefulness. Here, we use a generalized modeling framework to show that the degree of compensation can be related directly to the functional elasticity of growth, which is a general quantity that measures the change in recruitment relative to a change in biomass. We show that the elasticity of growth can be calculated from perturbations in fish biomass, is robust to observation error, and can be used to determine general attributes of the SRR in both continuous time production models, as well as discrete time age-structured models.
      PubDate: 2014-07-08
  • Multiple resource limitation: nonequilibrium coexistence of species in a
           competition model using a synthesizing unit
    • Abstract: Abstract During the last two decades, the simple view of resource limitation by a single resource has been changed due to the realization that co-limitation by multiple resources is often an important determinant of species growth. Hence, the multiple resource limitation hypothesis needs to be taken into account, when communities of species competing for resources are considered. We present a multiple species–multiple resource competition model which is based on the concept of synthesizing unit to formulate the growth rates of species competing for interactive essential resources. Using this model, we demonstrate that a more mechanistic explanation of interactive effects of co-limitation may lead to the known complex dynamics including nonequilibrium states as oscillations and chaos. We compare our findings with earlier investigations on biological mechanisms that can predict the outcome of multispecies competition. Moreover, we show that this model yields a periodic state where more species than limiting complementary resources can coexist (supersaturation) in a homogeneous environment. We identify two novel mechanisms, how such a state can emerge: a transcritical bifurcation of a limit cycle and a transition from a heteroclinic cycle. Furthermore, we demonstrate the robustness of the phenomenon of supersaturation when the environmental conditions are varied.
      PubDate: 2014-07-08
  • Trophic niche-space imaging, using resource and consumer traits
    • Abstract: Abstract The strength of trophic (feeding) links between two species depends on the traits of both the consumer and the resource. But which traits of consumer and resource have to be measured to predict link strengths, and how many? A novel theoretical framework for systematically determining trophic traits from empirical data was recently proposed. Here we demonstrate this approach for a group of 14 consumer fish species (Labeobarbus spp., Cyprinidae) and 11 aquatic resource categories coexisting in Lake Tana in northern Ethiopia, analysing large sets of phenotypic consumer and resource traits with known roles in feeding ecology. We systematically reconstruct structure and geometry of trophic niche space, in which link strengths are predicted by the distances between consumers and resources. These distances are then represented graphically resulting in an image of trophic niche space and its occupancy. We find trophic niche to be multidimensional. Among the models we analysed, one with two resource and two consumer traits had the highest predictive power for link strength. Results further suggest that trophic niche space has a pseudo-Euclidean geometry, meaning that link strength decays with distance in some dimensions of trophic niche space, while it increases with distance in other dimensions. Our analysis not only informs theory and modelling but may also be helpful for predicting trophic link strengths for pairs of other, similar species.
      PubDate: 2014-07-02
  • Modelling the dynamics of invasion and control of competing green crab
    • Abstract: Abstract Establishment of invasive species is a worldwide problem. In many jurisdictions, management strategies are being developed in an attempt to reduce the environmental and economic harm these species may cause in the receiving ecosystem. Scientific studies to improve understanding of the mechanisms behind invasive species population growth and spread are key components in the development of control methods. The work presented herein is motivated by the case of the European green crab (Carcinus maenas L.), a remarkably adaptable organism that has invaded marine coastal waters around the globe. Two genotypes of European green crab have independently invaded the Atlantic coast of Canada. One genotype invaded the mid-Atlantic coast of the USA by 1817, subsequently spreading northward through New England and reaching Atlantic Canada by 1951. A second genotype, originating from the northern limit of the green crabs European range, invaded the Atlantic coast of Nova Scotia in the 1980s and is spreading southward from the Canadian Maritime provinces. We developed an integrodifference equation model for green crab population growth, competition and spread, and demonstrate that it yields appropriate spread rates for the two genotypes, based on historical data. Analysis of our model indicates that while harvesting efforts have the benefit of reducing green crab density and slowing the spread rate of the two genotypes, elimination of the green crab is virtually impossible with harvesting alone. Accordingly, a green crab fishery would be sustainable. We also demonstrate that with harvesting and restocking, the competitive imbalance between the Northern and Southern green crab genotypes can be reversed. That is, a competitively inferior species can be used to control a competitively superior one.
      PubDate: 2014-06-21
  • Floquet theory for seasonal environmental forcing of spatially explicit
           waterborne epidemics
    • Abstract: Abstract The transmission of waterborne pathogens is a complex process that is heavily linked to the spatial characteristics of the underlying environmental matrix as well as to the temporal variability of the relevant hydroclimatological drivers. In this work, we propose a time-varying, spatially explicit network model for the dynamics of waterborne diseases. Applying Floquet theory, which allows to extend results of local stability analysis to periodic dynamical systems, we find conditions for pathogen invasion and establishment in systems characterized by fluctuating environmental forcing, thus extending to time-varying contexts the generalized reproduction numbers recently obtained for spatially explicit epidemiology of waterborne disease. We show that temporal variability may have multifaceted effects on the invasion threshold, as it can either favor pathogen invasion or make it less likely. Moreover, environmental fluctuations characterized by distinctive geographical signatures can produce diversified, highly nontrivial effects on pathogen invasion. Our study is complemented by numerical simulations, which show that pathogen establishment is neither necessary nor sufficient for large epidemic outbreaks to occur in time-varying environments. Finally, we show that our framework can be used to reliably characterize the early geography of epidemic outbreaks triggered by fluctuating environmental conditions.
      PubDate: 2014-06-13
  • Are time delays always destabilizing? Revisiting the role of time
           delays and the Allee effect
    • Abstract: Abstract One of the main challenges in ecology is to determine the cause of population fluctuations. Both theoretical and empirical studies suggest that delayed density dependence instigates cyclic behavior in many populations; however, underlying mechanisms through which this occurs are often difficult to determine and may vary within species. In this paper, we consider single species population dynamics affected by the Allee effect coupled with discrete time delay. We use two different mathematical formulations of the Allee effect and analyze (both analytically and numerically) the role of time delay in different feedback mechanisms such as competition and cooperation. The bifurcation value of the delay (that results in the Hopf bifurcation) as a function of the strength of the Allee effect is obtained analytically. Interestingly, depending on the chosen delayed mechanism, even a large time delay may not necessarily lead to instability. We also show that, in case the time delay affects positive feedback (such as cooperation), the population dynamics can lead to self-organized formation of intermediate quasi-stationary states. Finally, we discuss ecological implications of our findings.
      PubDate: 2014-06-03
  • Evolution of acuteness in pathogen metapopulations: conflicts between
           “classical” and invasion-persistence trade-offs
    • Abstract: Abstract Classical life-history theory predicts that acute, immunizing pathogens should maximize between-host transmission. When such pathogens induce violent epidemic outbreaks, however, a pathogen’s short-term advantage at invasion may come at the expense of its ability to persist in the population over the long term. Here, we seek to understand how the classical and invasion-persistence trade-offs interact to shape pathogen life-history evolution as a function of the size and structure of the host population. We develop an individual-based infection model at three distinct levels of organization: within an individual host, among hosts within a local population, and among local populations within a metapopulation. We find a continuum of evolutionarily stable pathogen strategies. At one end of the spectrum—in large well-mixed populations—pathogens evolve to greater acuteness to maximize between-host transmission: the classical trade-off theory applies in this regime. At the other end of the spectrum—when the host population is broken into many small patches—selection favors less acute pathogens, which persist longer within a patch and thereby achieve enhanced between-patch transmission: the invasion-persistence trade-off dominates in this regime. Between these extremes, we explore the effects of the size and structure of the host population in determining pathogen strategy. In general, pathogen strategies respond to evolutionary pressures arising at both scales.
      PubDate: 2014-04-29
  • Partitioning of trait variation among communities: measures of
           apportionment and differentiation based on binary sampling
    • Abstract: Abstract The notion that trait variation is partitioned among communities essentially rests on the supposition that the total variation in the metacommunity exceeds the variation within the communities due to differences between their trait distributions (the partitioning principle). Two elementary perspectives of partitioning can be distinguished: apportionment (members of the same community tend to hold the same trait state) and differentiation (members of different communities tend to hold different trait states). While the apportionment perspective reaches its extreme when each community is monomorphic (fixation), the differentiation perspective does so if communities share no trait states. Even though both perspectives can be shown to be involved in the analysis of community dynamics, their assessment is still almost completely limited to the apportionment perspective (chiefly G ST and its relatives). To overcome this limitation, methods of quantifying both partitioning perspectives are developed for qualitatively and quantitatively varying traits, where variation is represented by the differences in type resulting from sampling two individuals. It is shown that the validity of the partitioning principle and the design of corresponding measures crucially depend on proper specification of the modes of sampling and specification of differences between types that follow a concavity principle. This approach allows comparison between measures of apportionment and measures of differentiation. Such comparisons enable conclusions about the share that random (drift) and directional (selection, migration) processes have in the partitioning of variation among communities. One of the more far-reaching conclusions is that effects of forces apportioning variation outperform the effects of forces of differentiation, if the average similarity within communities exceeds the average difference between them.
      PubDate: 2014-04-11
  • Conflict between dynamical and evolutionary stability in simple ecosystems
    • Abstract: Abstract Here, we address the essential question of whether, in the context of evolving populations, ecosystems attain properties that enable persistence of the ecosystem itself. We use a simple ecosystem model describing resource, producer, and consumer dynamics to analyze how evolution affects dynamical stability properties of the ecosystem. In particular, we compare resilience of the entire system after allowing the producer and consumer populations to evolve to their evolutionarily stable strategy (ESS) to the maximum attainable resilience. We find a substantial reduction in ecosystem resilience when producers and consumers are allowed to evolve compared to the maximal attainable resilience. This study illustrates the inherent difference and possible conflict between maximizing individual-level fitness and maximizing resilience of entire ecosystems.
      PubDate: 2014-03-20
  • Phenologically explicit models for studying plant–pollinator
           interactions under climate change
    • Abstract: Abstract Climate change is significantly influencing phenology. One potential effect is that historically interacting partners will respond to climate change at different rates, creating the potential for a phenological mismatch among previously synchronized interacting species, or even sexes of the same species. Focusing on plant demographics in a plant–pollinator interaction, we develop a hybrid dynamical model that uses a “non-autonomous” differential equation system (Zonneveld model) for within-season dynamics and discrete equations for season-to-season dynamics. Our model outlines how and when changes in the relative phenologies of an interacting species pair will alter the demographic outcome of the interaction. For our plant–pollinator system, we find that plant population growth rates are particularly sensitive to phenology mismatch when flowers are short-lived, when pollinators are short-lived, or when flowers and pollinators exhibit high levels of within-population synchrony in emergence or arrival dates. More generally, our aim is to introduce the use of hybrid dynamical models as a framework through which researchers can directly explore the demographic consequences of climatically driven phenological change.
      PubDate: 2014-02-22
  • Individual variability and mortality required for constant final yield in
           simulated plant populations
    • Abstract: Abstract When plant monocultures are sown over a wide range of densities for a given period of time, the total biomass yield increases with density at low densities and then levels off at high densities, a phenomenon called constant final yield (CFY). There are several reported cases, however, where the total yield decreases at very high densities, but the reasons for such exceptions are not known. We used a spatially explicit, individual-based “field of neighborhood” simulation model to investigate the potential roles of spatial pattern, individual variation, and competitive stress tolerance for CFY. In the model, individual plants compete asymmetrically for light when their fields overlap, and this competition decreases growth and increases mortality. We varied (1) the initial size variation, (2) the spatial pattern, and (3) ability to survive intense competition and examined the effects on the density-biomass relationship. CFY was always observed when there was high variability among individuals, but not always when variability was low. This high size variation could be the result of high initial size variability or variation in the degree of local crowding. For very different reasons, very high and very low tolerance for competition resulted in decreasing total biomass at very high densities. Our results emphasize the importance of individual variation for population processes and suggest that we should look for exceptions to CFY in homogeneous, even-aged, regularly spaced populations such as plantations.
      PubDate: 2014-02-12
  • Nile perch (Lates niloticus,        class="a-plus-plus">L.) and cichlids (       class="a-plus-plus">Haplochromis spp.) in Lake Victoria:
           could prey mortality promote invasion of its predator'
    • Abstract: Abstract The invasion of Nile perch into Lake Victoria is one of the iconic examples of the destructive effect of an introduced species on an ecosystem but no convincing explanation exists of why Nile perch only increased dramatically after a 25 year lag. Here, we consider this problem using a mathematical model that takes into account interactions between Nile perch and its cichlid prey. We examined competing hypotheses to explain Nile perch invasion and show that suppression of juvenile Nile perch by cichlids may cause the system to have two alternative stable states: one with only cichlids and one with coexistence of cichlids and Nile perch. Without cichlid predation on Nile perch, alternative stable states did not occur. Our analysis indicates that cichlid mortality, for example fishing mortality, may have induced the observed shift between the states.
      PubDate: 2014-02-01
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