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  Subjects -> ENVIRONMENTAL STUDIES (Total: 781 journals)
    - ENVIRONMENTAL STUDIES (717 journals)
    - POLLUTION (21 journals)
    - WASTE MANAGEMENT (8 journals)

ENVIRONMENTAL STUDIES (717 journals)            First | 1 2 3 4 5 6 7 8     

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: 5)
Management of Environmental Quality: An International Journal     Hybrid Journal   (Followers: 4)
Management of Sustainable Development     Open Access   (Followers: 1)
Marine Ecology     Hybrid Journal   (Followers: 13)
Marine Environmental Research     Hybrid Journal   (Followers: 12)
Marine Pollution Bulletin     Hybrid Journal   (Followers: 12)
Materials for Renewable and Sustainable Energy     Open Access   (Followers: 8)
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: 9)
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: 7)
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: 283)
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  
Neurotoxicology and Teratology     Hybrid Journal   (Followers: 1)
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: 7)
Ocean Acidification     Open Access  
Ochrona Srodowiska i Zasobów Naturalnych     Open Access  
Oecologia     Hybrid Journal   (Followers: 29)
Oikos     Hybrid Journal   (Followers: 32)
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: 18)
Pace Environmental Law Review     Open Access   (Followers: 4)
Palaeobiodiversity and Palaeoenvironments     Hybrid Journal   (Followers: 3)
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: 9)
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: 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: 8)
Policy Studies Journal     Hybrid Journal   (Followers: 5)
Polish Polar Research     Open Access   (Followers: 4)
Political Studies     Hybrid Journal   (Followers: 23)
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: 8)
Postcolonial Studies     Hybrid Journal   (Followers: 9)
Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management     Full-text available via subscription   (Followers: 2)
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: 2)
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: 5)
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: 5)
Public Works Management & Policy     Hybrid Journal   (Followers: 6)
Qatar Foundation Annual Research Forum Proceedings     Open Access   (Followers: 3)
Radioactivity in the Environment     Full-text available via subscription   (Followers: 3)
Regional Environmental Change     Hybrid Journal   (Followers: 4)
Regional Studies     Hybrid Journal   (Followers: 6)
Religious Studies     Hybrid Journal   (Followers: 10)
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: 15)
Rendiconti Lincei     Hybrid Journal  
Renewable Energy Focus     Full-text available via subscription   (Followers: 8)
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)

  First | 1 2 3 4 5 6 7 8     

Journal Cover Theoretical Ecology     [SJR: 1.37]   [H-I: 10]
   [12 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  [2210 journals]
  • 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: 2015-01-25
  • Population spread in patchy landscapes under a strong Allee effect
    • Abstract: Abstract Many species of invasive insects establish and spread in regions around the world, causing enormous economical and environmental damage, in particular in forests. Some of these insects are subject to an Allee effect whereby the population must surpass a certain threshold in order to establish. Recent studies have examined the possibility of exploiting an Allee effect to improve existing control strategies. Forests and most other ecosystems show natural spatial variation, and human activities frequently increase the degree of spatial heterogeneity. It is therefore imperative to understand how the interplay between this spatial variation and individual movement behavior affects the overall speed of spread of an invasion. To this end, we study an integrodifference equation model in a patchy landscape and with Allee growth dynamics. Movement behavior of individuals varies according to landscape quality. Our study focuses on how the speed of the resulting traveling periodic wave depends on the interaction between landscape fragmentation, patch-dependent dispersal, and Allee population dynamics.
      PubDate: 2015-01-21
  • 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: 2015-01-17
  • Interactions among mutualism, competition, and predation foster species
           coexistence in diverse communities
    • Abstract: Abstract In natural systems, organisms are simultaneously engaged in mutualistic, competitive, and predatory interactions. Theory predicts that species persistence and community stability are feasible when the beneficial effects of mutualisms are balanced by density-dependent negative feedbacks. Enemy-mediated negative feedbacks can foster plant species coexistence in diverse communities, but empirical evidence remains mixed. Disparity between theoretical expectations and empirical results may arise from the effects of mutualistic mycorrhizal fungi. Here, we build a multiprey species/predator model combined with a bidirectional resource exchange system, which simulates mutualistic interactions between plants and fungi. To reach population persistence, (1) the per capita rate of increase of all plant population must exceed the sum of the negative per capita effects of predation, interspecific competition, and costs of mycorrhizal association, and (2) the per capita numerical response of enemies to mycorrhizal plants must exceed the magnitude of the per capita enemy rate of mortality. These conditions reflect the balance between regulation and facilitation in the system. Interactions between plant natural enemies and mycorrhizal fungi lead to shifts in the strength and direction of net mycorrhizal effects on plants over time, with common plant species deriving greater benefits from mycorrhizal associations than rare plant species.
      PubDate: 2015-01-16
  • Immigration can destabilize tri-trophic interactions: implications for
           conservation of top predators
    • Abstract: Abstract Top predators often have large home ranges and thus are especially vulnerable to habitat loss and fragmentation. Increasing connectance among habitat patches is therefore a common conservation strategy, based in part on models showing that increased migration between subpopulations can reduce vulnerability arising from population isolation. Although three-dimensional models are appropriate for exploring consequences to top predators, the effects of immigration on tri-trophic interactions have rarely been considered. To explore the effects of immigration on the equilibrium abundances of top predators, we studied the effects of immigration in the three-dimensional Rosenzweig-MacArthur model. To investigate the stability of the top predator equilibrium, we used MATCONT to perform a bifurcation analysis. For some combinations of model parameters with low rates of top predator immigration, population trajectories spiral towards a stable focus. Holding other parameters constant, as immigration rate is increased, a supercritical Hopf bifurcation results in a stable limit cycle and thus top predator populations that cycle between high and low abundances. Furthermore, bistability arises as immigration of the intermediate predator is increased. In this case, top predators may exist at relatively low abundances while prey become extinct, or for other initial conditions, the relatively higher top predator abundance controls intermediate predators allowing for non-zero prey population abundance and increased diversity. Thus, our results reveal one of two outcomes when immigration is added to the model. First, over some range of top predator immigration rates, population abundance cycles between high and low values, making extinction from the trough of such cycles more likely than otherwise. Second, for relatively higher intermediate predator migration rates, top predators may exist at low values in a truncated system with impoverished diversity, again with extinction more likely.
      PubDate: 2015-01-14
  • 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: 2014-12-27
  • 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: 2014-12-13
  • Patterns in intraspecific interaction strengths and the stability of food
    • Abstract: Abstract A common approach to analyse stability of biological communities is to calculate the interaction strength matrix. Problematic in this approach is defining intraspecific interaction strengths, represented by diagonal elements in the matrix, due to a lack of empirical data for these strengths. Theoretical studies have shown that an overall increase in these strengths enhances stability. However, the way in which the pattern in intraspecific interaction strengths, i.e. the variation in these strengths between species, influences stability has received little attention. We constructed interaction strength matrices for 11 real soil food webs in which four patterns for intraspecific interaction strengths were chosen, based on the ecological literature. These patterns included strengths that were (1) similar for all species, (2) trophic level dependent, (3) biomass dependent, or (4) death rate dependent. These four patterns were analysed for their influence on (1) ranking food webs by their stability and (2) the response in stability to variation of single interspecific interaction strengths. The first analysis showed that ranking the 11 food webs by their stability was not strongly influenced by the choice of diagonal pattern. In contrast, the second analysis showed that the response of food web stability to variation in single interspecific interaction strengths was sensitive to the choice of diagonal pattern. Notably, stability could increase using one pattern and decrease using another. This result asks for deliberate approaches to choose diagonal element values in order to make predictions on how particular species, interactions, or other food web parameters affect food web stability.
      PubDate: 2014-12-07
  • 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: 2014-12-02
  • 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: 2014-11-21
  • A niche remedy for the dynamical problems of neutral theory
    • Abstract: Abstract We demonstrate how niche theory and Hubbell’s original formulation of neutral theory can be blended together into a general framework modeling the combined effects of selection, drift, speciation, and dispersal on community dynamics. This framework connects many seemingly unrelated ecological population models and allows for quantitative predictions to be made about the impact of niche stabilizing and destabilizing forces on population extinction times and abundance distributions. In particular, the existence of niche stabilizing forces in our blended framework can simultaneously resolve two major problems with the dynamics of neutral theory, namely predictions of species lifetimes that are too short and species ages that are too long.
      PubDate: 2014-11-13
  • 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: 2014-11-01
  • Evolutionary dynamics through multispecies competition
    • Abstract: Abstract Disruptive selection, emerging from frequency-dependent intraspecific competition can have very exciting evolutionary outcomes. One such outcome is the origin of new species through an evolutionary branching event. Literature on theoretical models investigating the emergence of disruptive selection is vast, with some investigating the sensitivity of the models on assumptions of the competition and carrying capacity functions’ shapes. What is seldom modeled is what happens once the population escapes its effect via increase phenotypic or genotypic variance. The expectation is mixed: disruptive selection could diminish and ultimately disappear or it could still exist leading to further speciation events through multiple evolutionary branching events. Here, we derive the conditions under which disruptive selection drives two subpopulations that originated at a branching point to other points in trait space where each subpopulation again experiences disruptive selection. We show that the general pattern for further branchings require that the competition function to be even narrower than what is required for the first evolutionary branching. However, we also show that the existence of disruptive selection in higher dimensional systems is also sensitive to the shapes of the functions used.
      PubDate: 2014-11-01
  • Composite temporal strategies in pathogen evolution: balancing invasion
           and persistence
    • Abstract: Abstract There is ongoing interest in the conditions that favor the evolution of acute, highly transmissible infections in contrast to chronic ones. Earlier studies typically consider the evolution of a trait that is constant over the lifetime of an infection. However, for many pathogens, such traits can vary over this course. Here, we address the evolution of temporal patterns in limited host population sizes, where a trade-off between invasion and persistence can arise. This is of particular relevance to questions on the evolution of acuteness and chronicity. We ask whether population dynamics of transmission at the between-host level could lead pathogen adaptation to favor temporal strategies during the course of infection. To do this, we consider an infection to be composed of multiple stages, allowing each of these to evolve independently under a transmission–duration trade-off. We only consider selection taking place on the between-host level and examine the balance of invasion and persistence (i.e., maximizing replication vs. minimizing vulnerability to extinction), using several fitness-related measures. We find that a composite strategy that is ordered in time can confer higher fitness than any single, constant, strategy. We discuss the relevance of these results for the ordered expression of var genes in Plasmodium falciparum, as well as for infections that characteristically have several stages as in some bacterial pathogens.
      PubDate: 2014-11-01
  • Distinguishing intrinsic limit cycles from forced oscillations in
           ecological time series
    • Abstract: Abstract Ecological cycles are ubiquitous in nature and have triggered ecologists’ interests for decades. Deciding whether a cyclic ecological variable, such as population density, is part of an intrinsically emerging limit cycle or simply driven by a varying environment is still an unresolved issue, particularly when the only available information is in the form of a recorded time series. We investigate the possibility of discerning intrinsic limit cycles from oscillations forced by a cyclic environment based on a single time series. We argue that such a distinction is possible because of the fundamentally different effects that perturbations have on the focal system in these two cases. Using a set of generic mathematical models, we show that random perturbations leave characteristic signatures on the power spectrum and autocovariance that differ between limit cycles and forced oscillations. We quantify these differences through two summary variables and demonstrate their predictive power using numerical simulations. Our work demonstrates that random perturbations of ecological cycles can give valuable insight into the underlying deterministic dynamics.
      PubDate: 2014-11-01
  • Resource availability determines stability for
           mutualist–pathogen–host interactions
    • Abstract: Abstract Traditional explorations of interspecific interactions have generated extensive bodies of theory on mutualism and disease independently, but few studies have considered the interaction between them. We developed a model exploring the interactions among a fungal mutualist, a viral pathogen, and their shared plant host. Both microbes were assumed to alter the uptake and use of nutrients by the plant. We found that the productivity of the system and the strength of the plant–fungal mutualism influenced community dynamics. In particular, at low productivity, the pathogen may depend on the presence of the fungal mutualist for persistence. Furthermore, under some conditions, both the productivity of the system and the strength of the plant–fungal mutualism may simultaneously cause the mutualist to go extinct. We note the presence of cyclic plant–pathogen population dynamics only in the presence of the mutualist. As found in other models of consumer–resource interactions, cyclic dynamics were driven by high productivity, but, in contrast to simpler systems, high pathogen effectiveness did not consistently lead to cyclic dynamics. In total, association with mutualists can alter host–pathogen interactions, and the reverse is also true in that pathogens may alter host–mutualist interactions.
      PubDate: 2014-10-22
  • 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
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