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  Subjects -> ENVIRONMENTAL STUDIES (Total: 832 journals)
    - ENVIRONMENTAL STUDIES (758 journals)
    - POLLUTION (24 journals)
    - TOXICOLOGY AND ENVIRONMENTAL SAFETY (40 journals)
    - WASTE MANAGEMENT (10 journals)

ENVIRONMENTAL STUDIES (758 journals)            First | 1 2 3 4 5 6 7 8     

Journal of Southern African Studies     Hybrid Journal   (Followers: 7)
Journal of Sustainable Development     Open Access   (Followers: 12)
Journal of Sustainable Development Studies     Open Access   (Followers: 9)
Journal of Sustainable Society     Open Access   (Followers: 6)
Journal of the American Planning Association     Hybrid Journal   (Followers: 22)
Journal of the Association of Environmental and Resource Economists     Full-text available via subscription  
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 27)
Journal of the IEST     Full-text available via subscription  
Journal of the North Atlantic     Full-text available via subscription   (Followers: 1)
Journal of Theological Studies     Open Access   (Followers: 10)
Journal of Tropical Ecology     Hybrid Journal   (Followers: 11)
Journal of Urban and Environmental Engineering     Open Access   (Followers: 1)
Journal of Vietnamese Environment     Open Access   (Followers: 2)
Journal of Water Security     Open Access  
Journal of Wetlands Environmental Management     Open Access   (Followers: 1)
Julius-Kühn-Archiv     Open Access  
Kleio     Full-text available via subscription   (Followers: 2)
Knowledge Management Research & Practice     Hybrid Journal   (Followers: 18)
Koedoe : African Protected Area Conservation and Science     Open Access   (Followers: 7)
L1-Educational Studies in Language and Literature     Open Access   (Followers: 2)
Lake and Reservoir Management     Hybrid Journal   (Followers: 5)
Landscape Ecology     Hybrid Journal   (Followers: 44)
Landscapes     Hybrid Journal   (Followers: 18)
Large Marine Ecosystems     Full-text available via subscription  
Latin American and Caribbean Ethnic Studies     Hybrid Journal   (Followers: 5)
Latin American Journal of Management for Sustainable Development     Hybrid Journal   (Followers: 1)
Legal Studies     Hybrid Journal   (Followers: 4)
Letras Verdes. Revista Latinoamericana de Estudios Socioambientales     Open Access  
Leviathan : A Journal of Melville Studies     Full-text available via subscription   (Followers: 2)
Limnological Review     Open Access   (Followers: 6)
Living Reviews in Landscape Research     Open Access   (Followers: 2)
Local Environment: The International Journal of Justice and Sustainability     Hybrid Journal   (Followers: 7)
Low Carbon Economy     Open Access   (Followers: 4)
Luna Azul     Open Access  
M+A. Revista Electrónica de Medioambiente     Open Access  
Macquarie Journal of International and Comparative Environmental Law     Full-text available via subscription   (Followers: 9)
Madagascar Conservation & Development     Open Access  
Management International Review     Hybrid Journal   (Followers: 7)
Management of Environmental Quality: An International Journal     Hybrid Journal   (Followers: 6)
Management of Sustainable Development     Open Access   (Followers: 2)
Marine Ecology     Hybrid Journal   (Followers: 22)
Marine Environmental Research     Hybrid Journal   (Followers: 21)
Marine Pollution Bulletin     Hybrid Journal   (Followers: 22)
Materials for Renewable and Sustainable Energy     Open Access   (Followers: 10)
Mathematical and Computational Forestry & Natural-Resource Sciences     Free  
Mathematical Population Studies: An International Journal of Mathematical Demography     Hybrid Journal   (Followers: 2)
Medieval Sermon Studies     Hybrid Journal   (Followers: 3)
Medio Ambiente y Urbanizacion     Full-text available via subscription  
Membranes     Open Access   (Followers: 6)
Michigan Journal of Sustainability     Open Access  
Midwest Studies In Philosophy     Hybrid Journal   (Followers: 12)
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: 9)
Modern Cartography Series     Full-text available via subscription   (Followers: 4)
Mountain Research and Development     Open Access   (Followers: 4)
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: 7)
Nativa     Open Access  
Natur und Recht     Hybrid Journal   (Followers: 7)
Natural Areas Journal     Full-text available via subscription   (Followers: 9)
Natural Hazards     Hybrid Journal   (Followers: 118)
Natural Resources     Open Access  
Natural Resources and Environmental Issues     Open Access   (Followers: 5)
Nature and Culture     Full-text available via subscription   (Followers: 11)
NeuroToxicology     Hybrid Journal   (Followers: 1)
Neurotoxicology and Teratology     Hybrid Journal   (Followers: 1)
NEW SOLUTIONS: A Journal of Environmental and Occupational Health Policy     Full-text available via subscription   (Followers: 5)
New Zealand Journal of Environmental Law     Full-text available via subscription   (Followers: 4)
NJAS - Wageningen Journal of Life Sciences     Full-text available via subscription   (Followers: 1)
Noise Mapping     Open Access  
Noise Notes     Full-text available via subscription   (Followers: 3)
Novos Cadernos NAEA     Open Access   (Followers: 2)
Observatorio Medioambiental     Open Access  
Occupational and Environmental Medicine     Full-text available via subscription   (Followers: 10)
Ocean Acidification     Open Access   (Followers: 1)
Ochrona Srodowiska i Zasobów Naturalnych : Environmental Protection and Natural Resources     Open Access  
Oecologia     Hybrid Journal   (Followers: 44)
Oikos     Hybrid Journal   (Followers: 41)
Open Journal of Ecology     Open Access   (Followers: 10)
Open Journal of Marine Science     Open Access   (Followers: 7)
Open Journal of Modern Hydrology     Open Access   (Followers: 4)
Our Nature     Open Access   (Followers: 3)
Oxford Journal of Legal Studies     Hybrid Journal   (Followers: 22)
Pace Environmental Law Review     Open Access   (Followers: 6)
Pace Environmental Law Review Online Companion     Open Access   (Followers: 1)
Packaging, Transport, Storage & Security of Radioactive Material     Hybrid Journal   (Followers: 1)
Palaeobiodiversity and Palaeoenvironments     Hybrid Journal   (Followers: 4)
Particle and Fibre Toxicology     Open Access   (Followers: 2)
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: 3)
Planning & Environmental Law: Issues and decisions that impact the built and natural environments     Hybrid Journal   (Followers: 7)
Plant Ecology & Diversity     Partially Free   (Followers: 14)

  First | 1 2 3 4 5 6 7 8     

Journal Cover Theoretical Ecology
  [SJR: 1.456]   [H-I: 13]   [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  [2280 journals]
  • Coexistence and emergent neutrality generate synchrony among competitors
           in fluctuating environments
    • Abstract: Abstract Many competitive communities exhibit a puzzling amount of species diversity. In this study, we model a community of symmetric competitors in a fluctuating environment. We use biologically realistic temperature-dependent growth curves with a widely hypothesized trade-off between maximum growth and nice breadth to control the shapes of the curves of different species. We perform three analyses of the community dynamics to investigate the role of environmental fluctuations in community composition and species diversity. We initiate communities with equal abundances of all species and randomize the temperature fluctuations so that there is no correlation between species responses, only noise. We initiate single populations and allow other species to randomly invade the community. We also knock out extant species one by one from an established community and allow them to reinvade after the remaining species have adjusted. We find that competitors with sufficiently different temperature niches coexist via temporal niche differentiation. We also find long-term persistence of species that are very similar to a dominant competitor. This creates communities with species clumped along a temperature niche axis, with stable coexistence between groups and near neutrality within groups. The near neutrality results in interspecific synchrony within the groups, providing an explanation for the maintenance of high diversity in competitive communities where synchrony is commonly observed.
      PubDate: 2016-02-04
       
  • Introduction to the special issue: theory of food webs
    • PubDate: 2016-01-20
       
  • The ecology of asexual pairwise interactions: the generalized law of mass
           action
    • Abstract: Abstract A general procedure to formulate asexual (unstructured, deterministic) population dynamical models resulting from individual pairwise interactions is proposed. Individuals are characterized by a continuous strategy that is constant during life and represents their behavioral, morphological, and functional traits. Populations group conspecific individuals with identical strategy and are measured by densities in space. Species can be monomorphic, if only a single value of the strategy is present, or polymorphic otherwise. The procedure highlights the structural properties fulfilled by the population per-capita growth rates. In particular, the effect on the growth rate of jointly perturbing a set of similar strategies is proportional to the product of the corresponding densities, with a proportionality coefficient that can be density-dependent only through the sum of the densities. This generalizes the law of mass action, which traditionally refers to the case in which the per-capita growth rates are linearly density-dependent and insensitive to joint strategy perturbations. Being underpinned by individual strategies, the proposed procedure is most useful for evolutionary considerations, in the case strategies are inheritable. The developed body of theory is exemplified on a Holling-type-II many-prey-one-predator system and on a model of cannibalism.
      PubDate: 2016-01-15
       
  • Food web stability and weighted connectance: the complexity-stability
           debate revisited
    • Abstract: Abstract How the complexity of food webs relates to stability has been a subject of many studies. Often, unweighted connectance is used to express complexity. Unweighted connectance is measured as the proportion of realized links in the network. Weighted connectance, on the other hand, takes link weights (fluxes or feeding rates) into account and captures the shape of the flux distribution. Here, we used weighted connectance to revisit the relation between complexity and stability. We used 15 real soil food webs and determined the feeding rates and the interaction strength matrices. We calculated both versions of connectance, and related these structural properties to food web stability. We also determined the skewness of both flux and interaction strength distributions with the Gini coefficient. We found no relation between unweighted connectance and food web stability, but weighted connectance was positively correlated with stability. This finding challenges the notion that complexity may constrain stability, and supports the ‘complexity begets stability’ notion. The positive correlation between weighted connectance and stability implies that the more evenly flux rates were distributed over links, the more stable the webs were. This was confirmed by the Gini coefficients of both fluxes and interaction strengths. However, the most even distributions of this dataset still were strongly skewed towards small fluxes or weak interaction strengths. Thus, incorporating these distribution with many weak links via weighted instead of unweighted food web measures can shed new light on classical theories.
      PubDate: 2016-01-12
       
  • Predation risk tradeoffs in prey: effects on energy and behaviour
    • Abstract: Abstract The complexity of behavioural interactions in predator-prey systems has recently begun to capture trait-effects, or non-lethal effects, of predators on prey via induced behavioural changes. Non-lethal predation effects play crucial roles in shaping population and community dynamics, particularly by inducing changes to foraging, movement and reproductive behaviours of prey. Prey exhibit trade-offs in behaviours while minimizing predation risk. We use a novel evolutionary ecosystem simulation EcoSim to study such behavioural interactions and their effects on prey populations, thereby addressing the need for integrating multiple layers of complexity in behavioural ecology. EcoSim allows complex intra- and inter-specific interactions between behaviourally and genetically unique individuals called predators and prey, as well as complex predator-prey dynamics and coevolution in a tri-trophic and spatially heterogeneous world. We investigated the effects of predation risk on prey energy budgets and fitness. Results revealed that energy budgets, life history traits, allocation of energy to movements and fitness-related actions differed greatly between prey subjected to low-predation risk and high-predation risk. High-predation risk suppressed prey foraging activity, increased total movement and decreased reproduction relative to low-risk. We show that predation risk alone induces behavioural changes in prey which drastically affect population and community dynamics, and when interpreted within the evolutionary context of our simulation indicate that genetic changes accompanying coevolution have long-term effects on prey adaptability to the absence of predators.
      PubDate: 2015-12-30
       
  • Allee effects and resilience in stochastic populations
    • Abstract: Abstract Allee effects, or positive functional relationships between a population’s density (or size) and its per unit abundance growth rate, are now considered to be a widespread if not common influence on the growth of ecological populations. Here we analyze how stochasticity and Allee effects combine to impact population persistence. We compare the deterministic and stochastic properties of four models: a logistic model (without Allee effects), and three versions of the original model of Allee effects proposed by Vito Volterra representing a weak Allee effect, a strong Allee effect, and a strong Allee effect with immigration. We employ the diffusion process approach for modeling single-species populations, and we focus on the properties of stationary distributions and of the mean first passage times. We show that stochasticity amplifies the risks arising from Allee effects, mainly by prolonging the amount of time a population spends at low abundance levels. Even weak Allee effects become consequential when the ubiquitous stochastic forces affecting natural populations are accounted for in population models. Although current concepts of ecological resilience are bound up in the properties of deterministic basins of attraction, a complete understanding of alternative stable states in ecological systems must include stochasticity.
      PubDate: 2015-12-28
       
  • The “edge effect” phenomenon: deriving population abundance
           patterns from individual animal movement decisions
    • Abstract: Abstract Edge effects have been observed in a vast spectrum of animal populations. They occur where two conjoining habitats interact to create ecological phenomena that are not present in either habitat separately. On the individual-level, an edge effect is a change in behavioral tendency on or near the edge. On the population-level, it is a pattern of population abundance near an edge that cannot be explained in terms of either habitat in isolation. That these two levels of description exist suggests there ought to be a mathematical link between them. Here, we make inroads into providing such a link, deriving analytic expressions describing oft-observed population abundance patterns from a model of movement decisions near edges. Depending on the model parameters, we can see positive, negative, or transitional edge effects emerge. Importantly, the distance over which animals make their decisions to move between habitats turns out to be a key factor in quantifying the magnitude of certain observed edge effects.
      PubDate: 2015-12-23
       
  • Leading indicators of mosquito-borne disease elimination
    • Abstract: Abstract Mosquito-borne diseases contribute significantly to the global disease burden. High-profile elimination campaigns are currently underway for many parasites, e.g., Plasmodium spp., the causal agent of malaria. Sustaining momentum near the end of elimination programs is often difficult to achieve and consequently quantitative tools that enable monitoring the effectiveness of elimination activities after the initial reduction of cases has occurred are needed. Documenting progress in vector-borne disease elimination is a potentially important application for the theory of critical transitions. Non-parametric approaches that are independent of model-fitting would advance infectious disease forecasting significantly. In this paper, we consider compartmental Ross-McDonald models that are slowly forced through a critical transition through gradually deployed control measures. We derive expressions for the behavior of candidate indicators, including the autocorrelation coefficient, variance, and coefficient of variation in the number of human cases during the approach to elimination. We conducted a simulation study to test the performance of each summary statistic as an early warning system of mosquito-borne disease elimination. Variance and coefficient of variation were highly predictive of elimination but autocorrelation performed poorly as an indicator in some control contexts. Our results suggest that tipping points (bifurcations) in mosquito-borne infectious disease systems may be foreshadowed by characteristic temporal patterns of disease prevalence.
      PubDate: 2015-12-23
       
  • The migration game in habitat network: the case of tuna
    • Abstract: Abstract Long-distance migration is a widespread process evolved independently in several animal groups in terrestrial and marine ecosystems. Many factors contribute to the migration process and of primary importance are intra-specific competition and seasonality in the resource distribution. Adaptive migration in direction of increasing fitness should lead to the ideal free distribution (IFD) which is the evolutionary stable strategy of the habitat selection game. We introduce a migration game which focuses on migrating dynamics leading to the IFD for age-structured populations and in time varying habitats, where dispersal is costly. The model predicts migration dynamics between these habitats and the corresponding population distribution. When applied to Atlantic bluefin tunas, it predicts their migration routes and their seasonal distribution. The largest biomass is located in the spawning areas which have also the largest diversity in the age-structure. Distant feeding areas are occupied on a seasonal base and often by larger individuals, in agreement with empirical observations. Moreover, we show that only a selected number of migratory routes emerge as those effectively used by tunas.
      PubDate: 2015-12-22
       
  • Spatially heterogeneous pressure raises risk of catastrophic shifts
    • Abstract: Abstract Ecosystems may exhibit catastrophic shifts, i.e. abrupt and irreversible responses of ecosystem functions and services to continuous changes in external conditions. The search for early warning signs of approaching shifts has so far mainly been conducted on theoretical models assuming spatially-homogeneous external pressures (e.g. climatic). Here, we investigate how a spatially explicit pressure may affect ecosystems’ risk of catastrophic shifts and the associated spatial early-warning signs. As a case study, we studied a dryland vegetation model assuming ‘associational resistance’, i.e. the mutual reduction of local grazing impact by neighboring plants sharing the investment in defensive traits. Consequently, grazing pressure depends on the local density of plants and is thus spatially-explicit. We focus on the distribution of vegetation patch sizes, which can be assessed using remote sensing and are candidate early warning signs of catastrophic shifts in drylands. We found that spatially explicit grazing affected both the resilience and the spatial patterns of the landscape. Grazing impact became self-enhancing in more fragmented landscapes, disrupted patch growth and put apparently ‘healthy’ drylands under high risks of catastrophic shifts. Our study highlights that a spatially explicit pressure may affect the nature of the spatial pattern observed and thereby change the interpretation of the early warning signs. This may generalize to other ecosystems exhibiting self-organized spatial patterns, where a spatially-explicit pressure may interfere with pattern formation.
      PubDate: 2015-12-19
       
  • Interaction strength revisited—clarifying the role of energy flux
           for food web stability
    • Abstract: Abstract Interaction strength (IS) has been theoretically shown to play a major role in governing the stability and dynamics of food webs. Nonetheless, its definition has been varied and problematic, including a range of recent definitions based on biological rates associated with model parameters (e.g., attack rate). Results from food web theory have been used to argue that IS metrics based on energy flux ought to have a clear relationship with stability. Here, we use simple models to elucidate the actual relationship between local stability and a number of common IS metrics (total flux and per capita fluxes) as well as a more recently suggested metric. We find that the classical IS metrics map to stability in a more complex way than suggested by existing food web theory and that the new IS metric has a much clearer, and biologically interpretable, relationship with local stability. The total energy flux metric falls off existing theoretical predictions when the total resource productivity available to the consumer is reduced despite increased consumer attack rates. The density of a consumer can hence decrease when its attack rate increases. This effect, called the paradox of attack rate, is similar to the well-known hydra effect and can even cascade up a food chain to exclude a predator when consumer attack rate is increased.
      PubDate: 2015-11-23
       
  • Heterogeneity in patch quality buffers metapopulations from pathogen
           impacts
    • Abstract: Abstract Many wildlife species persist on a network of ephemerally occupied habitat patches connected by dispersal. Provisioning of food and other resources for conservation management or recreation is frequently used to improve local habitat quality and attract wildlife. Resource improvement can also facilitate local pathogen transmission, but the landscape-level consequences of provisioning for pathogen spread and habitat occupancy are poorly understood. Here, we develop a simple metapopulation model to investigate how heterogeneity in patch quality resulting from resource improvement influences long-term metapopulation occupancy in the presence of a virulent pathogen. We derive expressions for equilibrium host–pathogen outcomes in terms of provisioning effects on individual patches (through decreased patch extinction rates) and at the landscape level (the fraction of high-quality, provisioned patches), and highlight two cases of practical concern. First, if occupancy in the unprovisioned metapopulation is sufficiently low, a local maximum in occupancy occurs for mixtures of high- and low-quality patches, such that further increasing the number of high-quality patches both lowers occupancy and allows pathogen invasion. Second, if the pathogen persists in the unprovisioned metapopulation, further provisioning can result in all patches becoming infected and in a global minimum in occupancy. This work highlights the need for more empirical research on landscape-level impacts of local resource provisioning on pathogen dynamics.
      PubDate: 2015-11-04
       
  • The social benefits of private infectious disease-risk mitigation
    • Abstract: Abstract Does society benefit from private measures to mitigate infectious disease risks? Since mitigation reduces both peak prevalence and the number of people who fall ill, the answer might appear to be yes. But mitigation also prolongs epidemics and therefore the time susceptible people engage in activities to avoid infection. These avoidance activities come at a cost—in lost production or consumption, for example. Whether private mitigation yields net social benefits depends on the social weight given to the costs of illness and illness avoidance, now and into the future. We show that, for a large class of infectious diseases, private risk mitigation is socially beneficial. However, in cases where society discounts the future at either very low or very high rates relative to private individuals, or where it places a low weight on the private cost of illness, the social cost of illness under proportionate mixing (doing nothing) may be lower than the social cost of illness under preferential mixing (avoiding infectious individuals). That is, under some circumstances, society would prefer shorter, more intense epidemics without avoidance costs over longer, less intense epidemics with avoidance costs. A sobering (although not surprising) implication of this is that poorer societies should be expected to promote less private disease-risk mitigation than richer societies.
      PubDate: 2015-11-01
       
  • Sensitivity analysis of continuous-time models for ecological and
           evolutionary theories
    • Abstract: Abstract Sensitivity analyses are of paramount importance in ecological and evolutionary theories, but their application to continuous time models has been virtually ignored from these fields. We present a simple and general method that makes this analysis possible for any model specified by a system of ordinary differential equations, using the direct method from mathematical theory. The resulting analysis may be used to study the effect of parameter perturbation on the whole trajectories of the state variables as well as for deriving the sensitivity of composite metrics such as the population growth rate. We also present methods for analyzing the sensitivity of discrete events within a continuous-time framework, such as the age at maturation, where timing may be affected by the perturbation. These methods are applied to a model for the energetics of individual growth, reproduction, and mortality. The method is versatile and can be applied to study transient as well as asymptotic dynamics, and its application may benefit many fields of ecology and evolution.
      PubDate: 2015-11-01
       
  • The potential for alternative stable states in nutrient-enriched invaded
           grasslands
    • Abstract: Abstract Nutrient enrichment of native grasslands can promote invasion by exotic plant species, leading to reduced biodiversity and altered ecosystem function. Empirical evidence suggests that positive feedbacks may make such transitions difficult to reverse. We developed a mathematical model of grassland dynamics in which one group of species (native) is a better competitor for nitrogen (N) and another group (exotic) is a better competitor for light. We parameterized the model for a grassland community and reproduced observed transitions from a native- to an exotic-dominated state under N loading. Within known bounds of parameter values, both smooth and hysteretic transitions are plausible. The model also predicts that N loading alone is insufficient to achieve a transition to an exotic-dominated state on a timescale relevant to grassland management (a few decades), and that therefore some other disturbance (e.g., fire suppression or heaving grazing) must be present to accelerate it. The model predicts that to restore a grassland to a native-dominated state after N inputs have been reduced, fire and carbon supplements would be most effective. Further field research in N-enriched invaded grasslands is required to establish the strengths of positive feedbacks and, in turn, the consequences of anthropogenic modification of grasslands worldwide.
      PubDate: 2015-11-01
       
  • Rare niches and the ecological equivalence of species
    • Abstract: Abstract Debate remains on the contributions of niche and neutral processes in structuring biological communities. Temporal variation in the extent to which these two processes may jointly operate makes the problem of resolving their roles even more daunting. Here, we gain insight into this problem by using deterministic and stochastic models of competitors to investigate how the occurrence of rare niches, in what is usually a neutrally structured community, affects species diversity. Rare niches are modeled by allowing each species access to unique resources, which occur with temporal variability. While results from the deterministic model are clear (rare niches provide stable coexistence to otherwise neutral competitors), demographic stochasticity complicates this picture. Stochastic rare niche models show parameter regimes where increases in rare niches actually increase extinction risk by amplifying the variance in population counts. We also use our stochastic model to evaluate the effectiveness of current empirical methods in resolving the difference between rare niche and neutral systems. We find that in many cases, stochastic variation makes niche and neutral systems indistinguishable, allowing for the possibility of niche systems to masquerade as neutral ones. These results highlight the need to better understand how demographic stochasticity and environmental variation can affect the maintenance of species diversity.
      PubDate: 2015-11-01
       
  • Departures from neutrality induced by niche and relative fitness
           differences
    • Abstract: Abstract Breaking the core assumption of ecological equivalence in Hubbell’s “neutral theory of biodiversity” requires a theory of species differences. In one framework for characterizing differences between competing species, non-neutral interactions are said to involve both niche differences, which promote stable coexistence, and relative fitness differences, which promote competitive exclusion. We include both in a stochastic community model in order to determine if relative fitness differences compensate for changes in community structure and dynamics induced by niche differences, possibly explaining neutral theory’s apparent success. We show that species abundance distributions are sensitive to both niche and relative fitness differences, but that certain combinations of differences result in abundance distributions that are indistinguishable from the neutral case. In contrast, the distribution of species’ lifetimes, or the time between speciation and extinction, differs under all combinations of niche and relative fitness differences. The results from our model experiment are inconsistent with the hypothesis of “emergent neutrality” and support instead a hypothesis that relative fitness differences counteract effects of niche differences on distributions of abundance. However, an even more developed theory of interspecific variation appears necessary to explain the diversity and structure of non-neutral communities.
      PubDate: 2015-11-01
       
  • Resource distribution drives the adoption of migratory, partially
           migratory, or residential strategies
    • Abstract: Abstract Organismal movement can take on a variety of spatial and temporal forms. These forms depend in part on the type and scale of environment experienced as well as the internal state of the individual. However, individuals experiencing seemingly the same environment on the same time scale can display different movement strategies. While theorists have mathematically analyzed patch models and simulated spatially-explicit models, few studies have provided a mathematical analysis of migration in spatially-explicit models. Here, we consider a spatially explicit one-dimensional model where movement is costly and individuals must return to a common breeding ground annually to reproduce. We derive the optimal movement strategy, given specific movement costs and environmental resource distributions, obtaining closed-form solutions and results in several important special cases. We find, intuitively, that steep resource clines favor migratory behavior and shallow resource clines favor residential behavior, while lower movement efficiencies and shorter breeding cycles favor residency. However, we also show that when resource clines are sharp, migrants and residents can coinvade with each exploiting a locally optimal behavior. This can be interpreted as an example of partial migration (if migrants and residents are members of the same species). Alternatively, this can also be interpreted as two recently divergent species coinvading on a single resource, using different movement strategies to share the niche. We conclude with a discussion of density-dependent pressures on movement, including local resource depletion, and show that the density-independent results are relevant to density-dependent situations by calculating some stable strategy allocations analogous to ideal free distributions.
      PubDate: 2015-11-01
       
  • Combining mechanism and drift in community ecology: a novel statistical
           mechanics approach
    • Abstract: Abstract A key challenge for models of community ecology is to combine deterministic mechanism and stochastic drift in a systematic, transparent and tractable manner. Another challenge is to explain and unify different ecological patterns, hitherto modelled in isolation, within a single modelling framework. Here, we show that statistical mechanics provides an effective way to meet both challenges. We apply the statistical principle of maximum entropy (MaxEnt) to a simple resource-based, non-neutral model of a plant community. In contrast to previous ecological applications of MaxEnt, our use of MaxEnt emphasises its theoretical basis in the combinatorics of sampling frequencies, an approach that clarifies its ecological interpretation. In this approach, mechanism and drift are identified, respectively, with ecological resource constraints and entropy maximization. We obtain realistic predictions for species abundance distributions as well as contrasting stability-diversity relationships at community and population levels. The model also predicts critical behaviour that may provide a basis for understanding desertification and other ecological tipping points. Our results complement and extend previous ecological applications of MaxEnt to new areas of community ecology, and further illustrate MaxEnt as a powerful yet simple modelling tool for combining mechanism and drift in a way that unifies disparate ecological patterns.
      PubDate: 2015-11-01
       
  • A hypothetical model that explains differing net effects of inorganic
           fertilization on biomass and/or abundance of soil biota
    • Abstract: Abstract Researchers recently proposed a model describing the trade-offs between the positive and negative effects of nitrogen (N) fertilization on biomass and/or abundance of soil biota. The positive effects presumably result from the bottom-up influences of fertilizer-enhanced plant growth and from the improved soil habitat for soil biota. The negative effects presumably result from degradation of soil physico-chemical properties (e.g., salt effect, aluminum toxicity, calcium or magnesium deficiency, soil pH decline, and soil carbon resource availability reduction). The magnitude of these effects determines the net effect (or trade-off) of N fertilization on the biomass and/or abundance of soil biota. Our understanding of how positive and negative effects generate different net effects with changes in the N fertilization level is inadequate. In this paper, we propose two patterns of positive and negative effects (i.e., S-shaped and linear curves when the effects are plotted on fertilization level) and consider the many possibilities for the trade-offs. Specifically, there were 7 possible trade-offs between S-shaped positive effects and linear negative effects, 9 possibilities of the trade-off between linear positive effects and linear negative effects, 20 possibilities of the trade-off between S-shaped positive effects and S-shaped negative effects, and 9 possibilities of the trade-off between linear positive effects and S-shaped negative effects. In addition, the net effect might change or remain neutral (±), positive (+), or negative (−) with increasing nitrogen application. The hypothetical model could help explain the inconsistent results of the impacts of fertilization on soil biota reported in previous studies and could increase our understanding of the responses of soil biota to fertilization and other environmental disturbances.
      PubDate: 2015-11-01
       
 
 
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