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  Subjects -> ENVIRONMENTAL STUDIES (Total: 805 journals)
    - ENVIRONMENTAL STUDIES (736 journals)
    - POLLUTION (21 journals)
    - WASTE MANAGEMENT (9 journals)

ENVIRONMENTAL STUDIES (736 journals)            First | 1 2 3 4 5 6 7 8     

Knowledge Management Research & Practice     Hybrid Journal   (Followers: 20)
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: 4)
Landscape Ecology     Hybrid Journal   (Followers: 30)
Landscapes     Hybrid Journal   (Followers: 20)
Large Marine Ecosystems     Full-text available via subscription  
Latin American and Caribbean Ethnic Studies     Hybrid Journal   (Followers: 4)
Latin American Journal of Management for Sustainable Development     Hybrid Journal  
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: 8)
Madagascar Conservation & Development     Open Access  
Management International Review     Hybrid Journal   (Followers: 7)
Management of Environmental Quality: An International Journal     Hybrid Journal   (Followers: 5)
Management of Sustainable Development     Open Access   (Followers: 2)
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: 9)
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: 4)
Michigan Journal of Sustainability     Open Access  
Midwest Studies In Philosophy     Hybrid Journal   (Followers: 11)
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: 8)
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: 7)
Nativa     Open Access  
Natur und Recht     Hybrid Journal   (Followers: 7)
Natural Areas Journal     Full-text available via subscription   (Followers: 7)
Natural Hazards     Hybrid Journal   (Followers: 112)
Natural Resources     Open Access  
Natural Resources and Environmental Issues     Open Access   (Followers: 5)
Nature and Culture     Full-text available via subscription   (Followers: 10)
NeuroToxicology     Hybrid Journal   (Followers: 2)
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: 3)
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: 9)
Ocean Acidification     Open Access   (Followers: 1)
Ochrona Srodowiska i Zasobów Naturalnych : Environmental Protection and Natural Resources     Open Access  
Oecologia     Hybrid Journal   (Followers: 34)
Oikos     Hybrid Journal   (Followers: 34)
Open Journal of Ecology     Open Access   (Followers: 11)
Open Journal of Marine Science     Open Access   (Followers: 7)
Open Journal of Modern Hydrology     Open Access   (Followers: 3)
Our Nature     Open Access   (Followers: 3)
Oxford Journal of Legal Studies     Hybrid Journal   (Followers: 18)
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: 1)
Planning & Environmental Law: Issues and decisions that impact the built and natural environments     Hybrid Journal   (Followers: 7)
Plant Ecology & Diversity     Partially Free   (Followers: 13)
Plant Knowledge Journal     Open Access   (Followers: 2)
Plant, Cell & Environment     Hybrid Journal   (Followers: 5)
Polar Journal     Hybrid Journal   (Followers: 1)
Policy Studies     Hybrid Journal   (Followers: 7)
Policy Studies Journal     Hybrid Journal   (Followers: 4)
Polish Polar Research     Open Access   (Followers: 4)
Political Studies     Hybrid Journal   (Followers: 23)
Political Studies Review     Hybrid Journal   (Followers: 15)
Population and Environment     Hybrid Journal   (Followers: 6)
Population Ecology     Hybrid Journal   (Followers: 10)
Population Studies: A Journal of Demography     Hybrid Journal   (Followers: 8)
Postcolonial Studies     Hybrid Journal   (Followers: 10)
Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management     Full-text available via subscription   (Followers: 2)
Presence Teleoperators & Virtual Environments     Hybrid Journal   (Followers: 1)
Present Environment and Sustainable Development     Open Access  
Presidential Studies Quarterly     Hybrid Journal   (Followers: 3)
Procedia Environmental Sciences     Open Access   (Followers: 2)

  First | 1 2 3 4 5 6 7 8     

Journal Cover   Theoretical Ecology
  [SJR: 1.456]   [H-I: 13]   [10 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  [2281 journals]
  • Autochthonous or allochthonous resources determine the characteristic
           population dynamics of ecosystem engineers and their impacts
    • Abstract: Abstract Ecosystem engineering, or the modification of physical environments by organisms, can influence trophic interactions and thus food web dynamics. Although existing theory exclusively considers engineers using autochthonous resources, many empirical studies show that they often depend on allochthonous resources. By developing a simple mathematical model involving an ecosystem engineer that modifies the physical environment through its activities, its resource, and physical environment modified by the engineer, we compare the effects of autochthonous and allochthonous resources on the dynamics and stability of community with ecosystem engineers. To represent a variety of real situations, we consider engineers that alter either resource productivity, engineer feeding rate on the resource, or engineer mortality, and incorporate time-lagged responses of the physical environment. Our model shows that the effects of ecosystem engineering on community dynamics depend greatly on resource types. When the engineer consumes autochthonous resources, the community can exhibit oscillatory dynamics if the engineered environment affects engineer’s feeding rate or mortality. These cyclic behaviors are, however, stabilized by a slowly responding physical environment. When allochthonous resources are supplied as donor-controlled, on the other hand, the engineer population is unlikely to oscillate but instead can undergo unbounded growth if the engineered environment affects resource productivity or engineer mortality. This finding suggests that ecosystem engineers utilizing allochthonous resources may be more likely to reach high abundance and cause strong impacts on ecosystems. Our results highlight that community-based, compounding effects of trophic and physical biotic interactions of ecosystem engineers depend crucially on whether the engineers utilize autochthonous or allochthonous resources.
      PubDate: 2015-08-29
  • The phylogenetic component of food web structure and intervality
    • Abstract: Abstract Despite the exceptional complexity formed by species and their interactions in ecological networks, such as food webs, regularities in the network structures are repeatedly demonstrated. The interactions are determined by the characteristics of a species. The characteristics are in turn determined by the species’ phylogenetic relationships, but also by factors not related to evolutionary history. Here, we test whether species’ phylogenetic relationships provides a significant proxy for food web intervality. We thereafter quantify the degree to which different species traits remain valuable predictors of food web structure after the baseline effect of species’ relatedness has been removed. We find that the phylogenetic relationships provide a significant background from which to estimate food web intervality and thereby structure. However, we also find that there is an important, non-negligible part of some traits, e.g., body size, in food webs that is not accounted for by the phylogenetic relationships. Additionally, both these relationships differ depending if a predator or a prey perspective is adopted. Clearly, species’ evolutionary history as well as traits not determined by phylogenetic relationships shapes predator-prey interactions in food webs, and the underlying evolutionary processes take place on slightly different time scales depending on the direction of predator-prey adaptations.
      PubDate: 2015-08-04
  • Linking saturation, stability and sustainability in food webs with
           observed equilibrium structure
    • Abstract: Abstract Stability of a dynamic equilibrium in a predator-prey system depends both on the type of functional response and on the point of equilibrium on the response curve. Saturation effects from Holling type II responses are known to destabilise prey populations, while a type III (sigmoid) response curve has been shown to provide stability at lower levels of saturation. These effects have also been shown in multi-trophic model systems. However, stability analyses of observed equilibria in real complex ecosystems have as yet not assumed non-linear functional responses. Here, we evaluate the implications of saturation in observed balanced material-flow structures, for system stability and sustainability. We first make the effects of the non-linear functional responses on the interaction strengths in a food web transparent by expressing the elements of Jacobian ‘community’ matrices for type II and III systems as simple functions of their linear (type I) counterparts. We then determine the stability of the systems and distinguish two critical saturation levels: (1) a level where the system is just as stable as a type I system and (2) a level above which the system cannot be stable unless it is subsidised, separating a stable materially sustainable regime from an unsustainable one. We explain the stabilising and destabilising effects in terms of the feedbacks in the systems. The results shed light on the robustness of observed patterns of interaction strengths in complex food webs and suggest the implausibility of saturation playing a significant role in the equilibrium dynamics of sustainable ecosystems.
      PubDate: 2015-06-30
  • 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: 2015-06-13
  • The effect of predator avoidance and travel time delay on the stability of
           predator-prey metacommunities
    • Abstract: Abstract The stability conditions for an isolated specialist predator-prey community are fairly well understood. The spatial coupling of several such systems through dispersal of individuals can generate new dynamic behavior that is not yet completely understood. Many factors are known to be stabilizing or neutral, e.g., random dispersal or time delays, while others may induce instabilities in some cases but not others, e.g., density-dependent movement. We study the combination of two stabilizing mechanisms in a two-patch Rosenzweig-MacArthur model with a novel density-dependent movement term. Specifically, we assume that prey move between patches according to their perceived predation risk, and we include travel time between patches as a time delay. We show that the combination of mechanisms may be destabilizing even though each mechanism by itself is stabilizing. Our results show that a detailed knowledge of mechanisms and their temporal scales is necessary to correctly predict the stability of a metacommunity.
      PubDate: 2015-06-05
  • 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: 2015-06-04
  • The influence of host competition and predation on tick densities and
           management implications
    • Abstract: Abstract Host community composition and biodiversity can limit and regulate tick abundance which can have profound impacts on the incidence and severity of tick-borne diseases. Our understanding of the relationship between host community composition and tick abundance is still very limited. Here, we present a novel mathematical model of a stage-structured tick population to study the influence of host behaviour and competition in the presence of heterospecifics and the influence of host predation on tick densities. We examine the influence of specific changes in biodiversity that modify the competition among and the predation on small and large host populations. We find that increasing biodiversity will not always reduce tick populations, but depends on changes in species composition affecting the degree and type competition among hosts, and the host the predation is acting on. With indirect competition, tick densities are not regulated by increasing biodiversity; however, with direct competition, increased biodiversity will regulate tick densities. Generally, we find that biodiversity will regulate tick densities when it affects tick-host encounter rates. We also find that predation on small hosts have a limited influence on reducing tick populations, but when the predation was on large hosts this increased the magnitude of tick population oscillations. Our results have tick-management implications: while controlling large host populations (e.g. deer) and adult ticks will decrease tick densities, measures that directly control the nymph ticks could also be effective.
      PubDate: 2015-05-22
  • Mixotrophy: the missing link in consumer-resource-based ecologies
    • Abstract: Abstract The classical separate treatments of competition and predation and difficulties in providing a sensible theoretical basis for mutualism attest to the inability of traditional models to provide a synthesising framework for trophic interactions, a fundamental component of ecology. Recent approaches to food web modelling have focused on consumer–resource interactions. We construct a unifying theoretical framework to explicitly represent finite resources for each population using Lotka–Volterra (LV) equations. We show that mixotrophy, a ubiquitous trophic interaction in marine plankton, provides the key to developing a synthesis of the various ways of making a living. This framework also facilitates an explicit redefinition of facultative mutualism, illuminating the over-simplification of the traditional definition. We demonstrate a continuum between types of trophic interactions: populations can smoothly evolve through these types without losing stable coexistence. This provides a theoretical basis for the evolution of trophic interactions from autotrophy through mixotrophy/mutualism to heterotrophy.
      PubDate: 2015-05-01
  • Homing fidelity and reproductive rate for migratory populations
    • Abstract: Abstract Short-term and long-term population growth rates can differ considerably. While changes in growth rates can be driven by external factors, we consider another source for changes in growth rate. That is, changes are generated internally by gradual modification of population structure. Such a modification of population structure may take many generations, particularly when the populations are distributed spatially in heterogeneous environments. Here, the net reproductive rate R 0 is not sufficient to characterize short-term growth. Indeed, a population with net reproductive rate greater than one could initially decline precipitously, or a population with net reproductive rate less than one could initially grow substantially. Thus, we augment the net reproductive rate with lower and upper bounds for the transient reproductive rate, R l and R u . We apply these measures to the study of spatially structured salmon populations and show the effect of variable homing fidelity on short-term and long-term generational growth rates.
      PubDate: 2015-05-01
  • A unifying gravity framework for dispersal
    • Abstract: Abstract Most organisms disperse at some life-history stage, but different research traditions to study dispersal have evolved in botany, zoology, and epidemiology. In this paper, we synthesize concepts, principles, patterns, and processes in dispersal across organisms. We suggest a consistent conceptual framework for dispersal, which utilizes generalized gravity models. This framework will facilitate communication among research traditions, guide the development of dispersal models for theoretical and applied ecology, and enable common representation across taxonomic groups, encapsulating processes at the source and destination of movement, as well as during the intervening relocation process, while allowing each of these stages in the dispersal process to be addressed separately and in relevant detail. For different research traditions, certain parts of the dispersal process are less studied than others (e.g., seed release processes in plants and termination of dispersal in terrestrial and aquatic animals). The generalized gravity model can serve as a unifying framework for such processes, because it captures the general conceptual and formal components of any dispersal process, no matter what the relevant biological timescale involved. We illustrate the use of the framework with examples of passive (a plant), active (an animal), and vectored (a fungus) dispersal, and point out promising applications, including studies of dispersal mechanisms, total dispersal kernels, and spatial population dynamics.
      PubDate: 2015-05-01
  • Mean and variance of population density and temporal Taylor’s law in
           stochastic stage-structured density-dependent models of exploited fish
    • Abstract: Abstract How does fishing affect the mean and variance of population density in the presence of environmental fluctuations? Several recent authors have suggested that an increasing ratio of standard deviation to mean (coefficient of variation, or CV) in population density indicates declining population stability. We investigated the relationship between the mean and variance of population density in stochastic, density-dependent, stage-structured fish population models. Our models included either compensatory or overcompensatory density dependence affecting either fertility or juvenile survival. Environmental stochasticity affected either juvenile survival (when density dependence affected fertility) or fertility (when density dependence affected juvenile survival). The mean and variance of population density were compared as fishing mortality changed. In some cases, the relationship between the natural logarithms of mean and variance is linear under some parameters (life history strategy) of some models (the type of density dependence and the timing of density dependence and stochasticity), supporting Taylor’s law. In other cases, the relationship can be non-linear, especially when density dependence is overcompensatory, and depends on the stage observed. For example, the variance of adult density may increase with its mean while the variance of juvenile density of the same population may decline, or vice versa. The sequence in which individuals experience stochasticity and density dependence matters because density dependence can attenuate or magnify the fluctuation. In conclusion, the use of the CV as a proxy for population instability is not appropriate, and the CV of population density has to be interpreted carefully for other purposes.
      PubDate: 2015-05-01
  • Stochasticity and bistability in insect outbreak dynamics
    • Abstract: Abstract There is a long history in ecology of using mathematical models to identify deterministic processes that may lead to dramatic population dynamic patterns like boom-and-bust outbreaks. Stochasticity is also well-known to have a significant influence on the dynamics of many ecological systems, but this aspect has received far less attention. Here, we study a stochastic version of a classic bistable insect outbreak model to reveal the role of stochasticity in generating outbreak dynamics. We find that stochasticity has strong effects on the dynamics and that the stochastic system can behave in ways that are not easily anticipated by its deterministic counterpart. Both the intensity and autocorrelation of the stochastic environment are important. Stochasticity with higher intensity (variability) generally weakens bistability, causing the dynamics to spend more time at a single state rather than jumping between alternative stable states. Which state the population tends toward depends on the noise color. High-intensity white noise causes the insect population to spend more time at low density, potentially reducing the severity or frequency of outbreaks. However, red (positively autocorrelated) noise can make the population spend more time near the high density state, intensifying outbreaks. Under neither type of noise do early warning signals reliably predict impending outbreaks or population crashes.
      PubDate: 2015-05-01
  • The consequences of multiple indirect pathways of interaction for species
    • Abstract: Abstract Species in diverse communities typically have direct interactions with a small subset of other species, yet indirect effects can be traced between all of the species in a community. When multiple pathways of indirect effects link a pair of species, the magnitude and sign of the net effects depend on the details of the links in each indirect pathway. We explore the effects of alternative indirect pathways in a food web module that includes predation, competition, and mutualistic interactions; mutualisms are an important component of natural interaction networks, but are underrepresented in theoretical studies of indirect interactions. We use a conjugate variable method to partition the strength of a net indirect effect between two species that do not directly interact into two partial effects transmitted along two separate but simultaneously acting pathways: a pathway mediated by a shared predator and a pathway mediated by competing resources. Though the sign of each partial effect is generally negative, as expected, the strengths of the partial effects are different than if they occurred in isolation of one another. Summing the purely predator-mediated indirect effect and the purely resource-mediated indirect effect does not yield the net effect when they occur together. We find that when a resource-mediated pathway for an indirect effect is present, the presence of a shared predator can facilitate coexistence between apparent competitors, even allowing for the persistence of the species more vulnerable to predation. This approach holds promise for building a better understanding of the ways that indirect effects propagate through communities to affect patterns of relative abundance and coexistence.
      PubDate: 2015-05-01
  • The effects of maternal immunity and age structure on population immunity
           to measles
    • Abstract: Abstract Measles was successfully eradicated in the Pan-American Health Region in 2002. However, maintenance of elimination in parts of Africa, Europe, the USA, and other regions is proving difficult, despite apparently high vaccine coverage. This may be due to the different age structure in developed and developing populations, as well as to differences in the duration of maternal immunity. We explore the interaction between maternal immunity and age structure and quantify the resulting immunity gap between vaccine coverage and population immunity; we use this immunity gap as a novel metric of vaccine program success as it highlights the difference between actual and estimated immunity. We find that, for some combinations of maternal immunity and age structure, the accepted herd immunity threshold is not maintainable with a single-dose vaccine strategy for any combination of target age and coverage. In all cases, the herd immunity threshold is more difficult to maintain in a population with developing age structure. True population immunity is always improved if the target age at vaccination is chosen for the specific combination of maternal immunity and age structure.
      PubDate: 2015-05-01
  • Adaptive movement and food-chain dynamics: towards food-web theory without
           birth–death processes
    • Abstract: Abstract Population density can be affected by its prey [resource] and predator [consumer] abundances through two different mechanisms: the alternation of birth [or somatic growth] or death rate and inter-habitat movement. While the food-web theory has traditionally been built on the former mechanism, the latter mechanism has formed the basis of a successful theory explaining the spatial distribution of organisms in the context of behavioral and evolutionary ecology. Yet, few studies have compared these two mechanisms, leaving the question of how similar (or different) predictions derived from birth–death-based and movement-based food-web theories unanswered. Here, theoretical models of the tri-trophic (resource–consumer-top predator) food chain were used to compare food-web patterns arising from these two mechanisms. Specifically, we evaluated the response of the food-chain structure to inter-patch differences in productivity for movement-based models and birth–death-based models. Model analysis reveals that adaptive movements give rise to positively correlated responses of all trophic levels to increased productivity; however, this pattern was not observed in the corresponding birth–death-based model. The movement-based model predicts that the food chain response to productivity is determined by the sensitivity of animal movement to the environmental conditions. More specifically, increasing sensitivity of a consumer or top predator leads to smaller inter-patch variance of the resource or consumer density, while increasing inter-patch variance in the consumer or resource density. In conclusion, adaptive movement provides an alternative mechanism correlating the food-web structure to environmental conditions.
      PubDate: 2015-04-26
  • 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: 2015-04-19
  • 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: 2015-04-17
  • Departures from neutrality induced by niche and relative fitness
    • 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: 2015-04-08
  • The effects of space and diversity of interaction types on the stability
           of complex ecological networks
    • Abstract: Abstract The relationship between structure and stability in ecological networks and the effect of spatial dynamics on natural communities have both been major foci of ecological research for decades. Network research has traditionally focused on a single interaction type at a time (e.g. food webs, mutualistic networks). Networks comprising different types of interactions have recently started to be empirically characterized. Patterns observed in these networks and their implications for stability demand for further theoretical investigations. Here, we employed a spatially explicit model to disentangle the effects of mutualism/antagonism ratios in food web dynamics and stability. We found that increasing levels of plant-animal mutualistic interactions generally resulted in more stable communities. More importantly, increasing the proportion of mutualistic vs. antagonistic interactions at the base of the food web affects different aspects of ecological stability in different directions, although never negatively. Stability is either not influenced by increasing mutualism—for the cases of population stability and species’ spatial distributions—or is positively influenced by it—for spatial aggregation of species. Additionally, we observe that the relative increase of mutualistic relationships decreases the strength of biotic interactions in general within the ecological network. Our work highlights the importance of considering several dimensions of stability simultaneously to understand the dynamics of communities comprising multiple interaction types.
      PubDate: 2015-04-03
  • The effect of dispersal between patches on the stability of large trophic
           food webs
    • Abstract: Abstract Using computer simulations for the population dynamics of systems with many species, we investigate the stability of food webs distributed over several patches that are connected by migration. We evaluate the proportion of persisting species (robustness) and the probability that dynamics reach a fixed point in dependence of food-web complexity, patch arrangement, and migration rule. We find that migration in general increases robustness. This increase is strongest for intermediate migration rates and for star-like patch arrangements. The probability of reaching a fixed point decreases for intermediate migration rate, and has a large peak at larger migration rate for the star topology. We explain these various observations by the rescue effect, by dynamical coexistence of species, and by the buildup of biomass reservoirs in highly connected patches. As the species number becomes larger, differences between different patch arrangements become smaller, and the decrease in the probability of reaching a fixed point vanishes. This means that complex food webs are in some sense dynamically simpler than food webs consisting of less species.
      PubDate: 2015-02-13
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