The Experts below are selected from a list of 302322 Experts worldwide ranked by ideXlab platform
Peter Chesson - One of the best experts on this subject based on the ideXlab platform.
-
Effects of Predator Avoidance Behavior on the Coexistence of Competing Prey
The American naturalist, 2019Co-Authors: Pacifica Sommers, Peter ChessonAbstract:Predator avoidance behavior, in which prey limit foraging activities in the presence of predation threats, affects the dynamics of many ecological communities. Despite the growing theoretical appreciation of the role predation plays in Coexistence, predator avoidance behavior has yet to be incorporated into the theory in a general way. We introduce adaptive avoidance behavior to a consumer-resource model with three trophic levels to ask whether the ability of prey-the middle trophic level-to avoid predators alters their ability to coexist. We determine the characteristics of cases in which predator avoidance behavior changes prey Coexistence or the order of competitive dominance. The mechanism underlying such changes is the weakening of apparent competition relative to resource competition in determining niche overlap, even with resource intake costs. Avoidance behavior thus generally promotes Coexistence if prey partition resources but not predators, whereas it undermines Coexistence if prey partition predators but not resources. For any given case, the changes in the average fitness difference between two species resulting from avoidance behavior interact with changes in niche overlap to determine Coexistence. These results connect the substantial body of theoretical work on avoidance behavior and population dynamics with the body of theory on competitive Coexistence.
-
The relative importance of relative nonlinearity and the storage effect in the lottery model
Theoretical Population Biology, 2015Co-Authors: Chi Yuan, Peter ChessonAbstract:Although it is likely that many Coexistence mechanisms contribute to maintenance of species diversity, most approaches to understanding species Coexistence proceed as if only one mechanism would be present. In studies of species Coexistence in a temporally fluctuating environment, the storage effect, believed to be the most important Coexistence mechanism, has been the focus. Although a different Coexistence mechanism—relative nonlinearity—is also predicted to arise frequently with environmental variation, its effect has been overshadowed by the storage effect. The relatively nonlinear growth rates on which the mechanism depends arise simply from differences in life history traits. Many kinds of temporal variation can then interact with these nonlinearity differences to create the relative nonlinearity Coexistence mechanism. Much is unknown about when this mechanism is important and its total neglect is not justified. Here, we use the lottery model to provide a much needed quantitative assessment of the relative and combined effects of relative nonlinearity and the storage effect. Our analysis takes advantage of recently developed techniques for quantifying Coexistence mechanisms when multiple mechanisms operate in concert. We find that relative nonlinearity is able to contribute substantially to species Coexistence in the lottery model when two conditions are satisfied: (1) species must differ greatly in their adult death rates, (2) sensitivity of recruitment to environmental variation must be greater for species with larger adult death rates. In addition, relative nonlinearity has a critical role in compensating for a weakened storage effect when there is high correlation between species in their responses to the varying environment. In some circumstances relative nonlinearity is stronger than the storage effect or is even the sole mechanism of Coexistence.
-
variation in moisture duration as a driver of Coexistence by the storage effect in desert annual plants
Theoretical Population Biology, 2014Co-Authors: Galen Holt, Peter ChessonAbstract:a b s t r a c t Temporal environmental variation is a leading hypothesis for the Coexistence of desert annual plants. Environmental variation is hypothesized to cause species-specific patterns of variation in germination, which then generates the storage effect Coexistence mechanism. However, it has never been shown how sufficient species differences in germination patterns for multispecies Coexistence can arise from a shared fluctuating environment. Here we show that nonlinear germination responses to a single fluctuating physical environmental factor can lead to sufficient differences between species in germination pattern for the storage effect to yield Coexistence of multiple species. We derive these nonlinear germination responses from experimental data on the effects of varying soil moisture duration. Although these nonlinearities lead to strong species asymmetries in germination patterns, the relative nonlinearity Coexistence mechanism is minor compared with the storage effect. However, these asymmetries mean that the storage effect can be negative for some species, which then only persist in the face of interspecific competition through average fitness advantages. This work shows how a low dimensional physical environment can nevertheless stabilize multispecies Coexistence when the species have different nonlinear responses to common conditions, as supported by our experimental data.
-
Coexistence and evolutionary dynamics mediated by seasonal environmental variation in annual plant communities
Theoretical Population Biology, 2013Co-Authors: Andrea Mathias, Peter ChessonAbstract:It is well established theoretically that competing species may coexist by having different responses to variation over time in the physical environment. Whereas previous theory has focused mostly on year-to-year environmental variation, we investigate how within-year variation can be the basis of species Coexistence. We ask also the important but often neglected question of whether the species differences that allow Coexistence are compatible with evolutionary processes. We seek the simplest circumstances that permit Coexistence based on within-year environmental variation, and then evaluate the robustness of Coexistence in the face of evolutionary forces. Our focus is on Coexistence of annual plant species living in arid regions. We first consider environmental variation of a very simple structure where a single pulse of rain occurs, and different species have different patterns of growth activity following the rain pulse. We show that Coexistence of two species is possible based on the storage effect Coexistence mechanism in this simplest of varying environments. We find an exact expression for the magnitude of the storage effect that allows the functioning of the Coexistence mechanism to be analyzed. However, in these simplest of circumstances, Coexistence in our models is not evolutionarily stable. Increasing the complexity of the environment to two rain pulses leads to evolutionarily stable species Coexistence, and a route to diversity via evolutionary branching. This demonstration of the compatibility of a Coexistence mechanism with evolutionary processes is an important step in assessing the likely importance of a mechanism in nature.
-
Interacting Coexistence mechanisms in annual plant communities: Frequency-dependent predation and the storage effect.
Theoretical Population Biology, 2010Co-Authors: Jessica J. Kuang, Peter ChessonAbstract:We study frequency-dependent seed predation (FDP) in a model of competing annual plant species in a variable environment. The combination of a variable environment and competition leads to the storage-effect Coexistence mechanism (SE), which is a leading hypothesis for Coexistence of desert annual plants. However, seed predation in such systems demands attention to Coexistence mechanisms associated with predation. FDP is one such mechanism, which promotes Coexistence by shifting predation to more abundant plant species, facilitating the recovery of species perturbed to low density. When present together, FDP and SE interact, undermining each other's effects. Predation weakens competition, and therefore weakens mechanisms associated with competition: here SE. However, the direct effect of FDP in promoting Coexistence can compensate or more than compensate for this weakening of SE. On the other hand, the environmental variation necessary for SE weakens FDP. With high survival of dormant seeds, SE can be strong enough to compensate, or overcompensate, for the decline in FDP, provided predation is not too strong. Although FDP and SE may simultaneously contribute to Coexistence, their combined effect is less than the sum of their separate effects, and is often less than the effect of the stronger mechanism when present alone.
Dominique Gravel - One of the best experts on this subject based on the ideXlab platform.
-
Species Coexistence in a variable world.
Ecology letters, 2011Co-Authors: Dominique Gravel, Frédéric Guichard, Michael E. HochbergAbstract:Ecology Letters (2011) 14: 828–839 Abstract The contribution of deterministic and stochastic processes to species Coexistence is widely debated. With the introduction of powerful statistical techniques, we can now better characterise different sources of uncertainty when quantifying niche differentiation. The theoretical literature on the effect of stochasticity on Coexistence, however, is often ignored by field ecologists because of its technical nature and difficulties in its application. In this review, we examine how different sources of variability in population dynamics contribute to Coexistence. Unfortunately, few general rules emerge among the different models that have been studied to date. Nonetheless, we believe that a greater understanding is possible, based on the integration of Coexistence and population extinction risk theories. There are two conditions for Coexistence in the presence of environmental and demographic variability: (1) the average per capita growth rates of all coexisting species must be positive when at low densities, and (2) these growth rates must be strong enough to overcome negative random events potentially pushing densities to extinction. We propose that critical tests for species Coexistence must account for niche differentiation arising from this variability and should be based explicitly on notions of stability and ecological drift.
-
Shade tolerance, canopy gaps and mechanisms of Coexistence of forest trees
Oikos, 2010Co-Authors: Dominique Gravel, Charles D. Canham, Marilou Beaudet, Christian MessierAbstract:The belief that canopy gaps are important for the maintenance of tree species diversity appears to be widespread, but there have been no formal theoretical models to assess under what conditions gap phase processes allow Coexistence. Much of the empirical research on niche differentiation in response to gaps has focused on evidence for an interspecific tradeoff between low light survival and high light growth. The objectives of this study are first to distinguish the possible mechanisms allowing Coexistence based on this tradeoff, and second, to explore their limitations. We present a theory of forest dynamics driven by small-scale disturbances as a special case of the theory of Coexistence in variable environments. We demonstrate that temporal and spatial heterogeneity in light conditions that results from canopy gaps can allow stable Coexistence as a result of three previously documented general mechanisms: 'relative non-linearity', 'the successional niche' and the 'storage effect'. We find that temporal fluctuations in light availability alone allow the stable Coexistence of only two species. Spatial variation in disturbance synchronicity and intensity allows three species to coexist in a narrow parameter space. The rate of extinction is, however, extremely slow and there is transient Coexistence of a larger number of species for a long period of time. We conclude that while the low light survival/high light growth tradeoff may be ubiquitous in forest tree species, it is unlikely to function as an important mechanism for the stable Coexistence of several tree species.
Jonathan M. Levine - One of the best experts on this subject based on the ideXlab platform.
-
Does deterministic Coexistence theory matter in a finite world
2018Co-Authors: Sebastian J. Schreiber, Jonathan M. Levine, Oscar Godoy, Nathan J. B. Kraft, Simon HartAbstract:Abstract Contemporary studies of species Coexistence are underpinned by deterministic models that assume that competing species have continuous (i.e. non-integer) densities, live in infinitely large landscapes, and coexist over infinite time horizons. By contrast, in nature species are composed of discrete individuals subject to demographic stochasticity, and occur in habitats of finite size where extinctions occur in finite time. One important consequence of these discrepancies is that metrics of species Coexistence derived from deterministic theory may be unreliable predictors of the duration of species Coexistence in nature. These Coexistence metrics include invasion growth rates and niche and competitive differences, which are now commonly applied in theoretical and empirical studies of species Coexistence. Here we test the efficacy of deterministic Coexistence metrics on the duration of species Coexistence in a finite world. We introduce new theoretical and computational methods to estimate Coexistence times in a stochastic counterpart of a classic deterministic model of competition. Importantly, we parameterized this model using experimental field data for 90 pairwise combinations of 18 species of annual plants, allowing us to derive biologically-informed estimates of Coexistence times for a natural system. Strikingly, we find that for species expected to deterministically coexist, habitat sizes containing only tens of individuals have predicted Coexistence times of greater than 1, 000 years. We also find that invasion growth rates explain 60% of the variation in intrinsic Coexistence times, reinforcing their general usefulness in studies of Coexistence. However, only by integrating information on both invasion growth rates and species’ equilibrium population sizes could most (> 99%) of the variation in species Coexistence times be explained. Moreover, because of a complex relationship between niche overlap/competitive differences and equilibrium population sizes, increasing niche overlap and increasing competitive differences did not always result in decreasing Coexistence times as deterministic theory would predict. Nevertheless, our results tend to support the informed use of deterministic theory for understanding the duration of species Coexistence, while highlighting the need to incorporate information on species’ equilibrium population sizes in addition to invasion growth rates.
-
A structural approach for understanding multispecies Coexistence
Ecological Monographs, 2017Co-Authors: Serguei Saavedra, Oscar Godoy, Nathan J. B. Kraft, Rudolf P. Rohr, Jordi Bascompte, Jonathan M. LevineAbstract:Although observations of species-rich communities have long served as a primary motivation for research on the Coexistence of competitors, the majority of our empirical and theoretical understanding comes from two-species systems. How much of the Coexistence observed in species-rich communities results from indirect effects among competitors that only emerge in diverse systems remains poorly understood. Resolving this issue requires simple, scalable, and intuitive metrics for quantifying the conditions for Coexistence in multispecies systems, and how these conditions differ from those expected based solely on pairwise interactions. To achieve these aims, we develop a structural approach for studying the set of parameter values compatible with n-species Coexistence given the geometric constraints imposed by the matrix of competition coefficients. We derive novel mathematical metrics analogous to stabilizing niche differences and fitness differences that measure the range of conditions compatible with multispecies Coexistence, incorporating the effects of indirect interactions emerging in diverse systems. We show how our measures can be used to quantify the extent to which the conditions for Coexistence in multispecies systems differ from those that allow pairwise Coexistence, and apply the method to a field system of annual plants. We conclude by presenting new challenges and empirical opportunities emerging from our structural metrics of multispecies Coexistence.
-
The effects of intransitive competition on Coexistence
Ecology letters, 2017Co-Authors: Laure Gallien, Jonathan M. Levine, Niklaus E. Zimmermann, Peter B. AdlerAbstract:Coexistence theory has been developed with an almost exclusive focus on interactions between two species, often ignoring more complex and indirect interactions, such as intransitive loops, that can emerge in competition networks. In fact, intransitive competition has typically been studied in isolation from other pairwise stabilising processes, and thus little is known about how intransitivity interacts with more traditional drivers of species Coexistence such as niche partitioning. To integrate intransitivity into traditional Coexistence theory, we developed a metric of growth rate when rare, Δri¯, to identify and quantify the impact of intransitive competition against a backdrop of pairwise stabilising niche differences. Using this index with simulations of community dynamics, we demonstrate that intransitive loops can both stabilise or destabilise species Coexistence, but the strength and importance of intransitive interactions are significantly affected by the length and the topology of these loops. We conclude by showing how Δri¯ can be used to evaluate effects of intransitivity in empirical studies. Our results emphasise the need to integrate complex mechanisms emerging from diverse interactions into our understanding of species Coexistence.
-
Phenotypic Plasticity and Species Coexistence
Trends in ecology & evolution, 2016Co-Authors: Martin M. Turcotte, Jonathan M. LevineAbstract:Ecologists are increasingly interested in predicting how intraspecific variation and changing trait values impact species interactions and community composition. For many traits, much of this variation is caused by phenotypic plasticity, and thus the impact of plasticity on species Coexistence deserves robust quantification. Partly due to a lack of sound theoretical expectations, empirical studies make contradictory claims regarding plasticity effects on Coexistence. Our critical review of this literature, framed in modern Coexistence theory, reveals that plasticity affects species interactions in ways that could impact stabilizing niche differences and competitive asymmetries. However, almost no study integrates these measures to quantify the net effect of plasticity on species Coexistence. To address this challenge, we outline novel empirical approaches grounded in modern theory.
Michael E. Hochberg - One of the best experts on this subject based on the ideXlab platform.
-
Species Coexistence in a variable world.
Ecology letters, 2011Co-Authors: Dominique Gravel, Frédéric Guichard, Michael E. HochbergAbstract:Ecology Letters (2011) 14: 828–839 Abstract The contribution of deterministic and stochastic processes to species Coexistence is widely debated. With the introduction of powerful statistical techniques, we can now better characterise different sources of uncertainty when quantifying niche differentiation. The theoretical literature on the effect of stochasticity on Coexistence, however, is often ignored by field ecologists because of its technical nature and difficulties in its application. In this review, we examine how different sources of variability in population dynamics contribute to Coexistence. Unfortunately, few general rules emerge among the different models that have been studied to date. Nonetheless, we believe that a greater understanding is possible, based on the integration of Coexistence and population extinction risk theories. There are two conditions for Coexistence in the presence of environmental and demographic variability: (1) the average per capita growth rates of all coexisting species must be positive when at low densities, and (2) these growth rates must be strong enough to overcome negative random events potentially pushing densities to extinction. We propose that critical tests for species Coexistence must account for niche differentiation arising from this variability and should be based explicitly on notions of stability and ecological drift.
Jie Zhang - One of the best experts on this subject based on the ideXlab platform.
-
Coexistence of lte laa and wi fi on 5 ghz with corresponding deployment scenarios a survey
IEEE Communications Surveys and Tutorials, 2017Co-Authors: Bolin Chen, Jiming Chen, Yuan Gao, Jie ZhangAbstract:Long term evolution (LTE) carrier aggregation with 5 GHz unlicensed national informational infrastructure band has been pointed out by the industry as a good solution to handle the rapidly increasing amounts of data traffic. To provide fair Coexistence of LTE-licensed assisted access (LTE-LAA) and Wi-Fi on 5 GHz, several Coexistence mechanisms have already been proposed. This paper provides a comprehensive survey of the Coexistence of LTE-LAA and Wi-Fi on 5 GHz with corresponding deployment scenarios. We first analyze Coexistence-related features of those two technologies, including motivation, LTE carrier aggregation with unlicensed band, LTE and Wi-Fi medium access control protocols comparison, Coexistence challenges and enablers, performance difference between LTE-LAA and Wi-Fi, as well as co-channel interference. Second, we further extensively discuss current considerations about the Coexistence of LTE-LAA and Wi-Fi. Third, influential factors for the classification of small cell scenarios, as well as four representative scenarios are investigated in detail. Then we explore a relatively smooth technical route for solving Coexistence-related problems, which practically takes features of a specific scenario as the base for designing deployment mode of LTE-LAA and/or Wi-Fi. A scenario-oriented decision making procedure for the Coexistence issue and the analysis on an example deployment scenario, including design and performance evaluation metrics focusing on the concept of the scenario-oriented Coexistence are presented. We finally forecast further research trends on the basis of our conclusion.
