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  Subjects -> ENVIRONMENTAL STUDIES (Total: 755 journals)
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ENVIRONMENTAL STUDIES (682 journals)

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Journal Cover Theoretical Ecology
  [SJR: 1.255]   [H-I: 19]   [8 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  [2335 journals]
  • Effects of strength and timing of harvest on seasonal population models:
           stability switches and catastrophic shifts
    • Authors: Eduardo Liz
      Abstract: Population abundance of many species is controlled by a combination of density-dependent processes during different periods of the annual cycle. In the context of population exploitation or conservation programs, sequential density dependence has the potential to dramatically change population responses to harvesting. Looking for a better understanding of the potential effects of harvesting on the dynamics of seasonal populations, we carry out a theoretical analysis of a discrete model for a semelparous population with an annual cycle involving three discrete density-dependent events: breeding, natural mortality, and harvesting. Our study reveals how the interplay between the model parameters determines the importance of harvest timing on stability and population abundance, especially when two nontrivial stable equilibria coexist. We address the possibility for compensatory mortality and report different forms of the hydra effect, including non-smooth ones due to catastrophic shifts. These drastic switches may include hysteresis, which has important implications for conservation goals. Regarding variability, we show that increasing the harvesting effort may either stabilize or destabilize the population, and these effects strongly depend on harvest timing and natural mortality rates. Our results also emphasize the importance of sampling populations after every discrete event occurs during one cycle. Indeed, though the dynamics are not affected by census timing, the model shows that changes in population abundance in response to changes in harvesting pressure are substantially different depending on when population is sampled. Thus, a manager would receive different (and sometimes contradictory) messages depending on census time, which could lead to managing mistakes.
      PubDate: 2016-12-15
      DOI: 10.1007/s12080-016-0325-9
       
  • Effects of strength and timing of harvest on seasonal population models:
           stability switches and catastrophic shifts
    • Authors: Eduardo Liz
      Abstract: Population abundance of many species is controlled by a combination of density-dependent processes during different periods of the annual cycle. In the context of population exploitation or conservation programs, sequential density dependence has the potential to dramatically change population responses to harvesting. Looking for a better understanding of the potential effects of harvesting on the dynamics of seasonal populations, we carry out a theoretical analysis of a discrete model for a semelparous population with an annual cycle involving three discrete density-dependent events: breeding, natural mortality, and harvesting. Our study reveals how the interplay between the model parameters determines the importance of harvest timing on stability and population abundance, especially when two nontrivial stable equilibria coexist. We address the possibility for compensatory mortality and report different forms of the hydra effect, including non-smooth ones due to catastrophic shifts. These drastic switches may include hysteresis, which has important implications for conservation goals. Regarding variability, we show that increasing the harvesting effort may either stabilize or destabilize the population, and these effects strongly depend on harvest timing and natural mortality rates. Our results also emphasize the importance of sampling populations after every discrete event occurs during one cycle. Indeed, though the dynamics are not affected by census timing, the model shows that changes in population abundance in response to changes in harvesting pressure are substantially different depending on when population is sampled. Thus, a manager would receive different (and sometimes contradictory) messages depending on census time, which could lead to managing mistakes.
      PubDate: 2016-12-15
      DOI: 10.1007/s12080-016-0325-9
       
  • Single species dynamics under climate change
    • Authors: Mauricio Tejo; Sebastián Niklitschek-Soto; Cristin Vásquez; Pablo A. Marquet
      Abstract: We propose a general mathematical model describing the growth and dispersal of a single species living in a 1-D spatially discrete array of habitat patches affected by a sustained and directional change in climate. Our model accounts for two important characteristics of the climate change phenomenon: (1) Scale dependency: different species may perceive the change in the environment as occurring at different rates because they perceive the environment at different scales, and (2) measure dependency: different species measure the environment differently in the sense that they may be sensible to or cue in on different aspects of it (e.g., maximum temperature, minimum temperature, accumulated temperature) which is associated with their physiological, ecological, and life history attributes, which renders some characteristics of the environment more biologically relevant than others. We show that the deterioration in the quality of habitable patches as a consequence of climate change drives the species to extinction when dispersal is not possible; otherwise, we proof and provide a numerical example that, depending on the velocity of climate change, the scale at which a species measures it, and the particular attribute of the environment that is more biologically relevant to the species under analysis, there is always a migration strategy that allows the persistence of the species such that it tracks its niche conditions through space, thus shifting its geographic range. Our mathematical analysis provides a general framework to analyze species’ responses to climate change as a relational property of a given species in interaction with a change in climate. In particular, we can analyze the persistence of species by taking into account the ways in which they measure and filter the environment. Indeed, one of our main conclusions is that there is not a single climate change but many, as it depends on the interaction between a particular species and climate. Thus, the problem is more complex than assumed by analytically tractable models of species responses to climate change.
      PubDate: 2016-12-14
      DOI: 10.1007/s12080-016-0321-0
       
  • An individual-based model of chaparral vegetation response to frequent
           wildfires
    • Authors: Timothy A. Lucas; Reanna A. Doña; Wancen Jiang; Garrett C. Johns; Dayna J. Mann; Cassandra Seubert; Noah B. C. Webster; Charlotte H. Willens; Stephen D. Davis
      Abstract: The Santa Monica Mountains are home to many species of chaparral shrubs that provide vegetative cover and whose deep roots contribute to the stability of the steep slopes. Recently, native chaparral have been threatened by an unprecedented drought and frequent wildfires in Southern California. Besides the damage from the wildfires themselves, there is the potential for subsequent structural losses due to erosion and landslides. In this paper, we develop a mathematical model that predicts the impact of drought and frequent wildfires on chaparral plant community structure. We begin by classifying chaparral into two life history types based on their response to wildfires. Nonsprouters are completely killed by a fire, but their seeds germinate in response to fire cues. Facultative sprouters survive by resprouting but also rely on seed germination for post-fire recovery. The individual-based model presented here simulates the growth, seed dispersal, and resprouting behavior of individual shrubs across two life history types as they compete for space and resources in a rectangular domain. The model also incorporates varying annual rainfall and fire frequency as well as the competition between plants for scarce resources. The parameters were fit using seedling and resprout survivorship data as well as point quarter sampling data from 1986 to 2014 at a biological preserve within the natural landscape of the Malibu campus of Pepperdine University. The simulations from our model reproduce the change in plant community structure at our study site which includes the local extinction of the nonsprouter Ceanothus megacarpus due to shortened fire return intervals. Our simulations predict that a combination of extreme drought and frequent wildfires will drastically reduce the overall density of chaparral, increasing the likelihood of invasion by highly flammable exotic grasses. The simulations further predict that the majority of surviving shrubs will be facultative sprouting species such as Malosma laurina.
      PubDate: 2016-12-13
      DOI: 10.1007/s12080-016-0324-x
       
  • Chaotic attractor in two-prey one-predator system originates from
           interplay of limit cycles
    • Authors: Fanny Groll; Hartmut Arndt; Alexander Altland
      Abstract: We investigate the appearance of chaos in a microbial 3-species model motivated by a potentially chaotic real world system (as characterized by positive Lyapunov exponents (Becks et al., Nature 435, 2005). This is the first quantitative model that simulates characteristic population dynamics in the system. A striking feature of the experiment was three consecutive regimes of limit cycles, chaotic dynamics and a fixed point. Our model reproduces this pattern. Numerical simulations of the system reveal the presence of a chaotic attractor in the intermediate parameter window between two regimes of periodic coexistence (stable limit cycles). In particular, this intermediate structure can be explained by competition between the two distinct periodic dynamics. It provides the basis for stable coexistence of all three species: environmental perturbations may result in huge fluctuations in species abundances, however, the system at large tolerates those perturbations in the sense that the population abundances quickly fall back onto the chaotic attractor manifold and the system remains. This mechanism explains how chaos helps the system to persist and stabilize against migration. In discrete populations, fluctuations can push the system towards extinction of one or more species. The chaotic attractor protects the system and extinction times scale exponentially with system size in the same way as with limit cycles or in a stable situation.
      PubDate: 2016-12-13
      DOI: 10.1007/s12080-016-0317-9
       
  • Dissecting the role of transitivity and intransitivity on coexistence in
           competing species networks
    • Authors: Julio M. Alcántara; Manuel Pulgar; Pedro J. Rey
      Abstract: It is well established that intransitively assembled interaction networks can support the coexistence of competing species, while transitively assembled (hierarchical) networks are prone to species loss through competitive exclusion. However, as the number of species grows, the complexity of ecological interaction networks grows disproportionately, and species can get involved simultaneously in transitive and intransitive groups of interactions. In such complex networks, the effects of intransitivity on species persistence are not straightforward. Dissecting networks into intransitive/transitive components can help us to understand the complex role that intransitivity may play in supporting species diversity. We show through simulations that those species participating in the largest group of intransitive interactions (the core of the network) have high probabilities of persisting in the long term. However, participation in a group of intransitive interactions other than the core does not always improve persistence. Likewise, participating in transitive interactions does not always decrease persistence because certain species (the satellites) transitively linked to the core have also a high persistence probability. Therefore, when networks contain transitive and intransitive structures, as it can be expected in real ecological networks, the existence of a large intransitive core of species can have a disproportionate positive effect on species richness.
      PubDate: 2016-12-09
      DOI: 10.1007/s12080-016-0323-y
       
  • Bimodal trait distributions with large variances question the reliability
           of trait-based aggregate models
    • Authors: Renato Mendes Coutinho; Toni Klauschies; Ursula Gaedke
      Abstract: Functionally diverse communities can adjust their species composition to altered environmental conditions, which may influence food web dynamics. Trait-based aggregate models cope with this complexity by ignoring details about species identities and focusing on their functional characteristics (traits). They describe the temporal changes of the aggregate properties of entire communities, including their total biomasses, mean trait values, and trait variances. The applicability of aggregate models depends on the validity of their underlying assumptions that trait distributions are normal and exhibit small variances. We investigated to what extent this can be expected to work by comparing an innovative model that accounts for the full trait distributions of predator and prey communities to a corresponding aggregate model. We used a food web structure with well-established trade-offs among traits promoting mutual adjustments between prey edibility and predator selectivity in response to selection. We altered the shape of the trade-offs to compare the outcome of the two models under different selection regimes, leading to trait distributions increasingly deviating from normality. Their biomass and trait dynamics agreed very well for stabilizing selection and reasonably well for directional selection, under which different trait values are favored at different times. However, for disruptive selection, the results of the aggregate model strongly deviated from the full trait distribution model that showed bimodal trait distributions with large variances. Hence, the outcome of aggregate models is reliable under ideal conditions but has to be questioned when confronted with more complex selection regimes and trait distributions, which are commonly observed in nature.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0297-9
       
  • The effects of predation on seasonally migrating populations
    • Authors: John G. Donohue; Petri T. Piiroinen
      Abstract: Interspecific interactions may occur for just a brief period each year before the populations involved become spatially separated. For instance, the range of a migrating population may overlap with that of a population of predators for a single season. In this work, we outline a framework for examining how this kind of ‘transient’ predation influences the dynamics of the prey population. A time-dependent switching system is used to partition the annual cycle into distinct segments. We then consider the effect of a single predatory interaction during a particular season, with the associated predators characterised as either generalists or specialists. We show that generalist predation potentially can allow multiple stable limit cycles to exist. Predation by specialists may cause prey abundance to oscillate over long time periods. This is shown to be a consequence of over-exploitation of newborn prey individuals. The habitat-based formulation extends naturally to the study of interannual variation in environmental conditions. We illustrate how such changes may cause migrant populations to undergo sudden changes in numbers that are not readily reversible.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0304-1
       
  • The content and availability of information affects the evolution of
           social-information gathering strategies
    • Authors: Eleanor Redstart Brush; Naomi Ehrich Leonard; Simon A. Levin
      Abstract: Social animals can gather information by observing the other members of their groups. Strategies for gathering this type of social information have many components. In particular, an animal can vary the number of other animals it observes. European starlings (Sturnus vulgaris) in flight pay attention to a number of neighbors that allows the flock to reach consensus quickly and robustly. The birds may do this because being in such a flock confers benefits on its members, or the birds may use the strategy that is individually beneficial without regard for the flock’s structure. To understand when individual-level optimization results in a group-level optimum, we develop a model of animals gathering social information about environmental cues, where the cue can be about either predators or resources, and we analyze two processes through which the number of neighbors changes over time. We then identify the number of neighbors the birds use when the two dynamics reach equilibrium. First, we find that the equilibrium number of neighbors is much lower when the birds are learning about the presence of resources rather than predators. Second, when the information is about the presence of predators, we find that the equilibrium number of neighbors increases as the information becomes more widespread. Third, we find that an optimization process converges on strategies that allow the flock to reach consensus when the information is about the presence of abundant resources, but not when it is about the presence of scarce resources or predators.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0301-4
       
  • Trait selection during food web assembly: the roles of interactions and
           temperature
    • Authors: Isabelle Gounand; Sonia Kéfi; Nicolas Mouquet; Dominique Gravel
      Abstract: Understanding the processes driving community assembly is a central theme in ecology, yet this topic is marginally studied in food webs. Bioenergetic models have been instrumental in the development of food web theory, using allometric relationships with body mass, temperature, and explicit energy flows. However, despite their popularity, little is known about the constraints they impose on assembly dynamics. In this study, we build on classical consumer–resource theory to analyze the implications of the assembly process on trait selection in food webs. Using bioenergetic models, we investigate the selective pressure on body mass and conversion efficiency and its dependence on trophic structure and temperature. We find that the selection exerted by exploitative competition is highly sensitive to how the energy fluxes are modeled. However, the addition of a trophic level consistently selects for smaller body masses of primary producers. An increase in temperature triggers important cascading changes in food webs via a reduction of producer biomass, which is detrimental to herbivore persistence. This affects the structure of trait distributions, which in turn strengthens the exploitative competition and the selective pressure on traits. Our results suggest that greater attention should be devoted to the effects of food web assembly on trait selection to understand the diversity and the functioning of real food webs, as well as their possible response to ongoing global changes.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0299-7
       
  • Species richness in a model with resource gradient
    • Authors: Michel Droz; Andrzej Pękalski
      Abstract: In order to study the dependence of the species richness on heterogeneity of the habitat, we introduce an extended model of annual plants which combines the features of the island model and of gradient heterogeneity resources. First, we consider a native population of plants living on a square lattice of linear size L. After equilibration of this native population, seeds of several different species j = 2, ... , k of annual plants invade the system; they compete among themselves and the native ones. The system is exposed to a one-dimensional water gradient, and each species is characterised by a tolerance to a surplus of water, τ(j). We study the influences of the properties of the gradient of the resource (GR) on the species richness (SR) present in the system. We have shown that the relation between GR and SR is not straightforward and that several cases could be distinguished: For a large class of control parameters, SR increases linearly with GR. However, when the values of the control parameters are such as to create wide inhabitable regions, the relation between SR and GR ceases to have a monotonic character. We have also demonstrated that the average species richness as a function of the resource availability has a hump shape. Our results can be simply explained within our model and are in agreement with several previous field and theoretical works.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0298-8
       
  • Evolutionary food web models: effects of an additional resource
    • Authors: Daniel Ritterskamp; Christoph Feenders; Daniel Bearup; Bernd Blasius
      Abstract: Many empirical food webs contain multiple resources, which can lead to the emergence of sub-communities—partitions—in a food web that are weakly connected with each other. These partitions interact and affect the complete food web. However, the fact that food webs can contain multiple resources is often neglected when describing food web assembly theoretically, by considering only a single resource. We present an allometric, evolutionary food web model and include two resources of different sizes. Simulations show that an additional resource can lead to the emergence of partitions, i.e. groups of species that specialise on different resources. For certain arrangements of these partitions, the interactions between them alter the food web properties. First, these interactions increase the variety of emerging network structures, since hierarchical bodysize relationships are weakened. Therefore, they could play an important role in explaining the variety of food web structures that is observed in empirical data. Second, interacting partitions can destabilise the population dynamics by introducing indirect interactions with a certain strength between predator and prey species, leading to biomass oscillations and evolutionary intermittence.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0305-0
       
  • Vaccine-driven evolution of parasite virulence and immune evasion in
           age-structured population: the case of pertussis
    • Authors: Veronika Bernhauerová
      Abstract: Despite enormous success of mass immunization programs in reducing incidence of infectious diseases, vaccine-escape strains have emerged perhaps as a consequence of strong selection pressures exerted on parasites by vaccines. Pertussis presents a well-documented example. As a childhood infection, it exhibits age-specific transmission biased to children. Assuming different transmission rates between children and adults, I study, by means of an age-structured epidemic model, evolutionary dynamics of parasite virulence in a vaccinated population. I find that the age-structure does not affect the evolutionary dynamics of parasite virulence. Also, based on empirical data reporting antigenic divergence with vaccine strains and mutations in virulence-associated genes in pertussis populations, I allow for parallel occurrence of mutations in parasite virulence and associated immune evasion. I conclude that this simultaneous adaptation of both traits may substantially alter the evolutionary course of the parasite. In particular, higher values of virulence are favoured once the parasite is able to evade the transmission-blocking vaccine-induced immunity. On the other hand, lower values of virulence are selected for once the parasite evolves the ability to evade the virulence-blocking vaccine-induced immunity. I emphasize the importance of multi-trait evolution to assess the direction of parasite adaptation more accurately.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0300-5
       
  • The duality of stability: towards a stochastic theory of species
           interactions
    • Authors: Gabriel Gellner; Kevin S. McCann; Alan Hastings
      Abstract: Understanding the dynamics of ecological systems using stability concepts has been a key driver in ecological research from the inception of the field. Despite the tremendous effort put into this area, progress has been limited due to the bewildering number of metrics used to describe ecological stability. Here, we seek to resolve some of the confusion by unfolding the dynamics of a simple consumer-resource interaction module. In what follows, we first review common dynamical metrics of stability (CV, eigenvalues). We argue using the classical type II consumer-resource model as an example where the empirical stability metric, CV, hides two different, but important, aspects of stability: (i) stability due to mean population density processes and (ii) stability due to population density variance processes. We then employ a simple stochastic consumer-resource framework in order to elucidate (i) when we expect these two different aspects of stability to arise in ecological systems and, importantly, highlight (ii) the fact that these two different aspects of stability respond differentially, but predictably, to changes in fundamental parameters that govern biomass flux and loss in any consumer-resource interaction (e.g., attack rates, carrying capacity, mortality).
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0303-2
       
  • Effects of diffusion on total biomass in heterogeneous continuous and
           discrete-patch systems
    • Authors: D. L. DeAngelis; Wei-Ming Ni; Bo Zhang
      Abstract: Theoretical models of populations on a system of two connected patches previously have shown that when the two patches differ in maximum growth rate and carrying capacity, and in the limit of high diffusion, conditions exist for which the total population size at equilibrium exceeds that of the ideal free distribution, which predicts that the total population would equal the total carrying capacity of the two patches. However, this result has only been shown for the Pearl-Verhulst growth function on two patches and for a single-parameter growth function in continuous space. Here, we provide a general criterion for total population size to exceed total carrying capacity for three commonly used population growth rates for both heterogeneous continuous and multi-patch heterogeneous landscapes with high population diffusion. We show that a sufficient condition for this situation is that there is a convex positive relationship between the maximum growth rate and the parameter that, by itself or together with the maximum growth rate, determines the carrying capacity, as both vary across a spatial region. This relationship occurs in some biological populations, though not in others, so the result has ecological implications.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0302-3
       
  • Coevolutionary dynamics in one-to-many mutualistic systems
    • Authors: Hideo Ezoe
      Abstract: “One-to-many” mutualisms are often observed in nature. In this type of mutualism, each host individual can interact with many symbionts, whereas each individual symbiont can interact with only one host individual. Partner choice by the host is a potentially critical mechanism for maintaining such systems; however, its long-term effects on the coevolution between the hosts and symbionts have not been completely explored. In this study, I developed a simple mathematical model to describe the coevolutionary dynamics between hosts and symbionts in a one-to-many mutualism. I assumed that each host chooses a constant number of symbionts from a potential symbiont population, a fraction of which are chosen through preferential choice on the basis of the cooperativeness of the symbionts and the rest are chosen randomly. Using numerical calculations, I found that mutualism is maintained when the preferential choice is not very costly and the mutation rate of symbionts is large. I also found that symbionts that receive benefits from hosts without a return (cheater symbionts) and hosts that do not engage in preferential partner choice (indiscriminator hosts) can coexist with mutualist symbionts and discriminator hosts, respectively. The parameter domain of pure mutualism, i.e., free from cheater symbionts and indiscriminator hosts, can be narrower than the whole domain where the mutualism persists.
      PubDate: 2016-12-01
      DOI: 10.1007/s12080-016-0296-x
       
  • Interspecific interactions and range limits: contrasts among interaction
           types
    • Authors: William Godsoe; Nathaniel J. Holland; Chris Cosner; Bruce E. Kendall; Angela Brett; Jill Jankowski; Robert D. Holt
      Abstract: There is a great deal of interest in the effects of biotic interactions on geographic distributions. Nature contains many different types of biotic interactions (notably mutualism, commensalism, predation, amensalism, and competition), and it is difficult to compare the effects of multiple interaction types on species’ distributions. To resolve this problem, we analyze a general, flexible model of pairwise biotic interactions that can describe all interaction types. In the absence of strong positive feedback, a species’ ability to be present depends on its ability to increase in numbers when it is rare and the species it is interacting with is at equilibrium. This insight leads to counterintuitive conclusions. Notably, we often predict the same range limit when the focal species experiences competition, predation, or amensalism. Similarly, we often predict the same range margin or when the species experiences mutualism, commensalism, or benefits from prey. In the presence of strong positive density-dependent feedback, different species interactions produce different range limits in our model. In all cases, the abiotic environment can indirectly influence the impact of biotic interactions on range limits. We illustrate the implications of this observation by analyzing a stress gradient where biotic interactions are harmful in benign environments but beneficial in stressful environments. Our results emphasize the need to consider the effects of all biotic interactions on species’ range limits and provide a systematic comparison of when biotic interactions affect distributions.
      PubDate: 2016-11-29
      DOI: 10.1007/s12080-016-0319-7
       
  • A slow-fast dynamic decomposition links neutral and non-neutral
           coexistence in interacting multi-strain pathogens
    • Authors: Erida Gjini; Sten Madec
      Abstract: Understanding the dynamics of multi-type microbial ecosystems remains a challenge, despite advancing molecular technologies for diversity resolution within and between hosts. Analytical progress becomes difficult when modelling realistic levels of community richness, relying on computationally-intensive simulations and detailed parametrisation. Simplification of dynamics in polymorphic pathogen systems is possible using aggregation methods and the slow-fast dynamics approach. Here, we develop one new such framework, tailored to the epidemiology of an endemic multi-strain pathogen. We apply Goldstone’s idea of slow dynamics resulting from spontaneously broken symmetries to study direct interactions in co-colonization, ranging from competition to facilitation between strains. The slow-fast dynamics approach interpolates between a neutral and non-neutral model for multi-strain coexistence, and quantifies the asymmetries that are important for the maintenance and stabilisation of diversity.
      PubDate: 2016-11-29
      DOI: 10.1007/s12080-016-0320-1
       
  • Effective competition determines the global stability of model ecosystems
    • Authors: Antonio Ferrera; Alberto Pascual-García; Ugo Bastolla
      Abstract: We investigate the stability of Lotka-Volterra (LV) models constituted by two groups of species such as plants and animals in terms of the intragroup effective competition matrix, which allows separating the equilibrium equations of the two groups. In matrix analysis, the effective competition matrix represents the Schur complement of the species interaction matrix. It has been previously shown that the main eigenvalue of this effective competition matrix strongly influences the structural stability of the model ecosystem. Here, we show that the spectral properties of the effective competition matrix also strongly influence the dynamical stability of the model ecosystem. In particular, a necessary condition for diagonal stability of the full system, which guarantees global stability, is that the effective competition matrix is diagonally stable, which means that intergroup interactions must be weaker than intra-group competition in appropriate units. For mutualistic or competitive interactions, diagonal stability of the effective competition is a sufficient condition for global stability if the inter-group interactions are suitably correlated, in the sense that the biomass that each species provides to (removes from) the other group must be proportional to the biomass that it receives from (is removed by) it. For a non-LV mutualistic system with saturating interactions, we show that the diagonal stability of the corresponding LV system close to the fixed point is a sufficient condition for global stability.
      PubDate: 2016-11-28
      DOI: 10.1007/s12080-016-0322-z
       
  • Maintaining cooperation in social-ecological systems:
    • Authors: Andrew R. Tilman; James R. Watson; Simon Levin
      Abstract: Natural resources are vulnerable to over-exploitation in the absence of effective management. However, norms, enforced by social ostracism, can promote cooperation and increase stock biomass in common-pool resource systems. Unfortunately, the long-term sustainable use of a resource is not assured even if cooperation, maintained by ostracism and aimed at optimizing resource use, exists. Here, using the example of fisheries, we show that for a cooperative to be maintained by ostracism over time, it often must act inefficiently, choosing a ‘second-best’ strategy where the resource is over-harvested to some degree. Those cooperatives that aim for maximum sustainable profit, the “first-best” harvest strategy, are more vulnerable to invasion by independent harvesters, leading to larger declines in the fish population. In contrast, second-best strategies emphasize the resistance to invasion by independent harvesters over maximizing yield or profit. Ultimately, this leads to greater long-run payoffs to the resource users as well as higher resource stock levels. This highlights the value of pragmatism in the design of cooperative institutions for managing natural resources.
      PubDate: 2016-11-26
      DOI: 10.1007/s12080-016-0318-8
       
  • Paradoxical effects and interactions in food webs: a commentary on Nilsson
           and McCann (2016)
    • Authors: Peter A. Abrams
      Abstract: Counter-intuitive responses of population density to changes in parameter values were used by Nilsson and McCann (Theor Ecol 9:59–71, 2016, Theoretical Ecology) to argue for the superiority of a recently proposed measure of interaction strength. They argued that one of these responses (decreasing consumer density in response to increasing per capita resource attack rate) is rarely or never discussed and is distinct from responses to consumer mortality. In fact, there is a long history of work on responses to altered attack rates, and they are linked to responses to mortality because the latter very often produce coupled changes in attack rate. This earlier literature does not support a qualitative difference between the impacts of these two types of parameter change and does not clearly support the desirability of any particular measure of interaction strength.
      PubDate: 2016-08-27
      DOI: 10.1007/s12080-016-0312-1
       
  • Erratum to: Role of trade-off between sexual and vertical routes for
           evolution of pathogen transmission
    • Authors: Veronika Bernhauerová; Luděk Berec
      PubDate: 2016-07-28
      DOI: 10.1007/s12080-016-0308-x
       
 
 
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