Ecology Competition and Coexistence in Animal Communities
by
Priyanga Amarasekare
  • LAST REVIEWED: 06 May 2016
  • LAST MODIFIED: 29 October 2013
  • DOI: 10.1093/obo/9780199830060-0017

Introduction

Competition is one of the most ubiquitous of species interactions. It occurs any time a resource that is essential to growth and reproduction (e.g., food, shelter, nesting sites) occurs in short supply. The acquisition of the resource by one individual simultaneously deprives others’ access to it, and this has a negative effect on the fitness of individuals and the per capita growth rates of populations. Competition is thus an interaction that has mutually negative effects on the participants. Coexistence results when populations of several species that utilize the same limiting resources manage to persist within the same locality. This article focuses on competitive coexistence in animal communities. Animals have two characteristics that determine the kinds of resources they can use and the mechanisms by which they can tolerate or avoid competition for these resources. First, animals are heterotrophs and have to ingest other organisms to obtain the energy required for growth and reproduction; competition thus involves biotic resources. Second, most animals are mobile and hence able to avoid or reduce competitive effects through dispersal.

Historical Overview

This section highlights the seminal work that laid the conceptual foundations and empirical investigations of competition and coexistence.

Early Classics

Verhulst 1838 developed the first mathematical model of competition that led the way for the now famous Lotka-Volterra model for inter-specific competition in Lotka 1925 and Volterra 1926. Pearl 1927 provided empirical support for Verhulst’s logistic model and the experimental work in Gause 1934 that led to the “Competitive Exclusion Principle,” which was motivated by the theory developed in Lotka 1925 and Volterra 1926. The laboratory experiments by Thomas Park (Park 1948) and field experiments by Joseph H. Connell (Connell 1961) were built on these earlier theories and experiments. Together, this body of work underlies much of what we understand about competition not only in the fields of ecology and evolution but also in economics, fisheries, and human demography.

  • Connell, J. H. 1961. The influence of inter-specific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42:710–723.

    DOI: 10.2307/1933500Save Citation »Export Citation »E-mail Citation »

    The oft-cited classic study of competition between two species of barnacles in Scotland. Connell demonstrated that the two species Chthamalus stellatus and Balanus balanoides competed via both exploitative and interference competition and that coexistence was possible because of spatial segregation driven by Balanus being superior at interference competition (via smothering and undercutting) and Chthamalus being superior at dessication resistance.

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    • Gause, G. F. 1934. The struggle for existence. Baltimore: Williams and Wilkins.

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      The classic work of Gause, based on his experiments on paramecium species and motivated by the mathematical theory of Lotka and Volterra, that led to the formulation of the competitive exclusion principle.

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      • Lotka, A. J. 1925. Elements of physical biology. Baltimore: Williams and Wilkins.

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        Derivation of the Lotka-Volterra competition model for two species that engage in intra- and inter-specific competition. A classical model that has withstood the test of time.

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        • Park, T. 1948. Experimental studies of interspecies competition. I. Competition between populations of flour beetles Tribolium confusum Duval and Tribolium castaneum Herbst. Ecological Monographs 18:265–308.

          DOI: 10.2307/1948641Save Citation »Export Citation »E-mail Citation »

          Using experiments with species of Tribolium species, Park showed that two species engaged in interference competition could not coexist and that the outcome of competition was indeterminate, i.e., depending on initial conditions one or the other species would win in competition. One of the very first empirical demonstrations of the priority effect.

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          • Pearl, R. 1927. The growth of populations. Quarterly Review of Biology 2:532–548.

            DOI: 10.1086/394288Save Citation »Export Citation »E-mail Citation »

            A classic paper demonstrating that population growth in both humans and animals can be described by a simple equation (the logistic, developed in Verhulst 1838) that contains only per capita birth and death rates.

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            • Verhulst, P. F. 1838. Notice sur la loi que la population sui dans son accroissement. Correspondences Mathematiques et Physiques 10:113–121.

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              The first formulation of a mathematical model to describe the population dynamical consequences of intra-specific competition in organisms with overlapping generations. Verhulst coined the term “logistic” to describe the differential equation describing the rate of population growth, which has since become a cornerstone in ecology, evolution, and economics.

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              • Volterra, V. 1926. Variazioni e fluttuazioni del numero d’individui in specie animali conviventi. Italy: Citta di Castello.

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                Independently derived the mathematical model for two competing species, which was later referred to as the Lotka-Volterra competition model.

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                Later Developments

                The 1970s and 1980s saw an explosion of new ideas and syntheses on competition and its importance for community structure. Foremost among these is Diamond 1973, a paper on competition in New Guinean birds, followed in Cody 1974 on North American birds; Hairston 1980 is a classic study on salamanders, and David Tilman’s seminal experiments on diatoms are described in Tilman 1977 and Tilman, et al. 1981. Two highly influential papers, Schoener 1983 and Connell 1983, evaluate the study of competition and its impact on the field and reach somewhat disparate conclusions. Diamond and Case 1986 summarizes a series of articles on theoretical and empirical work on competition that shaped the field in the 1970s and 1980s.

                • Cody, M. L. 1974. Competition and the structure of bird communities. Princeton, NJ: Princeton Univ. Press.

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                  Summarizes empirical information on the role of competition in structuring bird communities.

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                  • Connell, J. H. 1983. On the prevalence and relative importance of interspecific competition: Evidence from field experiments. American Naturalist 122:661–696.

                    DOI: 10.1086/284165Save Citation »Export Citation »E-mail Citation »

                    A much-cited paper, also based on a survey of the literature, that found weak evidence of inter-specific competition. Of historical interest, as reflecting an era in which doubt was cast on the role of competition and other ecological interactions as driving the dynamics and regulation of populations and communities.

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                    • Diamond, J. M. 1973. Distributional ecology of New Guinea birds. Science 19:759–769.

                      DOI: 10.1126/science.179.4075.759Save Citation »Export Citation »E-mail Citation »

                      Uses observational data of bird species’ distributions to argue that inter-specific competition has shaped their community structure in the islands of New Guinea.

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                      • Diamond, J., and T. J. Case. 1986. Community Ecology. Harper and Row: New York.

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                        Contains a series of influential articles that summarize contemporary thinking about competition and its consequences for community structure. While many of the articles are now outdated, they provide a historical perspective of how ideas about competition were shaping the field of ecology in the 1970s and 1980s.

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                        • Hairston, N. G. 1980. The experimental test of an analysis of field distributions: Competition in terrestrial salamanders. Ecology 61:817–826.

                          DOI: 10.2307/1936752Save Citation »Export Citation »E-mail Citation »

                          One of the best examples of competition in action in a natural community. Using field exclusion experiments, Hairston demonstrated ongoing competition between two salamander species inhabiting the southern Appalachian Mountains. Each species showed an increase in vital rates and/or abundances when the other species was removed, suggesting they are limited by inter-specific competition in sympatry.

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                          • Schoener, T. 1983. Field experiments on inter-specific competition. American Naturalist 122:240–285.

                            DOI: 10.1086/284133Save Citation »Export Citation »E-mail Citation »

                            An oft-cited paper (along with Connell 1983) during the 1980s debate on the importance of competition as a factor in driving population regulation and species diversity. This paper found strong evidence for the operation of inter-specific competition (both exploitative and interference) in natural communities.

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                            • Tilman, D. 1977. Resource competition between planktonic algae: An experimental and theoretical approach. Ecology 58:338–348.

                              DOI: 10.2307/1935608Save Citation »Export Citation »E-mail Citation »

                              Classic paper that provides empirical evidence and theoretical support for the resource ratio hypothesis: i.e., the idea that two species can coexist in the long term if each species is limited by a different resource.

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                              • Tilman, D, M. Mattson, and S. Langer. 1981. Competition and nutrient kinetics along a temperature gradient: An experimental test of a mechanistic approach to niche theory. Limnology and Oceanography 26:1020–1033.

                                DOI: 10.4319/lo.1981.26.6.1020Save Citation »Export Citation »E-mail Citation »

                                The empirical work on competition between two diatom species that motivated the development of the R* rule (see Primary Literature). The study was unusual in that it quantified the impact of each species on the limiting resource as well as species’ abundances. This allowed the authors to determine the mechanism of competitive exclusion: the species that reduced the resource to a lower level won in competition.

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                                Controversies and Resolutions

                                The 1970s and 1980s also saw the birth of a controversy about the role of competition in structuring communities. An alternative perspective was put forward, which argued that patterns of community structure could be explained by purely statistical models that assumed no species interactions. Connor and Simberloff 1979 proposes a null model for bird diversity patterns on islands as an alternative to Diamond 1975 and its hypothesis of competition. Gilpin and Diamond 1984 criticizes Connor and Simberloff’s approach, pointing out that the null model also contained elements of competition. Connor and Simberloff 1983 responded to these criticisms, and a long debate ensued. Harvey, et al. 1983 reviews the controversies surrounding the construction and use of null models in community ecology, and Gotelli and Graves 1996 provides an overview of the different types of null models used in ecological studies. In more recent developments, Gotelli 2000 compares different algorithms for null models to identify the conditions under which violations of model assumptions lead to nonrandom patterns.

                                • Connor, E. F., and D. Simberloff. 1979. The assembly of species communities: Chance or competition? Ecology 60:1132–1140.

                                  DOI: 10.2307/1936961Save Citation »Export Citation »E-mail Citation »

                                  Shows that the bird species distribution patterns studied by Diamond 1975 could be explained by a null model with no species interactions, thus questioning the role of competition in generating the observed patterns.

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                                  • Connor, E. F., and D. Simberloff. 1983. Interspecific competition and species co-occurrence patterns on islands: Null models and the evaluation of evidence. Oikos 41:455–465.

                                    DOI: 10.2307/3544105Save Citation »Export Citation »E-mail Citation »

                                    Constitutes a response to the criticisms of the null models in Gilpin and Diamond 1984 and points out that the major function of the null-model approach is to provide a null hypothesis (that species co-occurrence patterns are not different from that expected if they were distributed randomly) against which hypotheses about species interactions could be compared.

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                                    • Diamond, J. M. 1975. Assembly of species communities. In Ecology and evolution of communities. Edited by Martin L. Cody and Jared M. Diamond, 342–344. Cambridge, MA: Harvard Univ. Press.

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                                      Diamond hypothesized that inter-specific competition was the mechanism responsible for the nonoverlapping (checkerboard) patterns of bird species distributions on islands.

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                                      • Gilpin, M., and J. M. Diamond. 1984. Are species co-occurrences on islands nonrandom, and are null hypotheses useful in community ecology? In Ecological communities: Conceptual issues and the evidence. Edited by D. R. Strong, 297–315. Princeton, NJ: Princeton Univ. Press.

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                                        Pointed out that the null models developed in Connor and Simberloff 1979 were not truly null because model assumptions implicitly included competition. For instance, Connor and Simberloff assumed that the total number of species on an island was the same as the total number actually observed on the island, which number could well have been the result of competition.

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                                        • Gotelli, N. J. 2000. Null model analysis of species co-occurrence patterns. Ecology 81:2606–2621.

                                          DOI: 10.1890/0012-9658(2000)081[2606:NMAOSC]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

                                          Compares nine different algorithms for null models with respect to Type I and Type II errors to identify the conditions under which the null hypothesis of no species interactions would be incorrectly accepted or rejected.

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                                          • Gotelli, N. J., and G. R. Graves. 1996. Null models in ecology. Washington, DC: Smithsonian Institution.

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                                            Provides an overview of the different types of null models used to study species diversity, size ratios, species co-occurrence, and species-area relationships.

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                                            • Harvey, P., R. K. Colwell, J. W. Silvertown, and R. M. May. 1983. Null models in Ecology. Annual Review of Ecology and Systematics 14:189–211.

                                              DOI: 10.1146/annurev.es.14.110183.001201Save Citation »Export Citation »E-mail Citation »

                                              Discusses the controversies surrounding the construction and use of null models in various areas of community ecology. It focuses on the relevant biological question of interest, how null models can shed light of the questions, and the technical problems involved in finding the appropriate null model for a given question.

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                                              Basic Principles of Competition

                                              This section deals with Primary Literature on the basic principles of competition and the Conceptual Syntheses that have resulted from basic research on competition.

                                              Primary Literature

                                              MacArthur and Levins 1964 developed one of the first mathematical models of multispecies competition, and MacArthur and Levins 1967 formalized the idea of limiting similarity. Abrams 1983 expanded on the idea of limiting similarity while Tilman 1982 developed the R* theory: the idea that when two or more species are limited by the same resource, the species that can maintain a positive per capita growth rate at the lowest resource level will exclude all other species. Holt 1977 developed the idea of apparent competition. Jeffries and Lawton 1984 put forward the equivalent concept of enemy-free space, which was empirically demonstrated in Jeffries and Lawton 1985. Schmitt 1987 provides one of the first empirical examples of this phenomenon.

                                              • Abrams, P. A. 1983. The theory of limiting similarity. Annual Review of Ecology and Systematics 14:359–376.

                                                DOI: 10.1146/annurev.es.14.110183.002043Save Citation »Export Citation »E-mail Citation »

                                                A synthesis of ideas about limiting similarity and niche differentiation with insights on how the concept can be more usefully applied.

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                                                • Holt, R. D. 1977. Predation, apparent competition, and structure of prey communities. Theoretical Population Biology 12:197–229.

                                                  DOI: 10.1016/0040-5809(77)90042-9Save Citation »Export Citation »E-mail Citation »

                                                  An important paper demonstrating, with a formal mathematical model, that species that do not compete with one another can have mutually negative effects due to their sharing of a common predator. This phenomenon is called “apparent competition” and has since been found to be an important interaction in real communities.

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                                                  • Jeffries, M. J., and J. H. Lawton. 1984. Enemy-free space and the structure of ecological communities. Biological Journal of the Linnean Society 23:269–286.

                                                    DOI: 10.1111/j.1095-8312.1984.tb00145.xSave Citation »Export Citation »E-mail Citation »

                                                    Formulates the idea of competition for enemy-free space, the same dynamical phenomenon as apparent competition (see Holt 1977).

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                                                    • Jeffries, M. J., and J. H. Lawton. 1985. Predator-prey ratios in communities of freshwater invertebrates: The role of enemy-free space. Freshwater Biology 15:105–112.

                                                      DOI: 10.1111/j.1365-2427.1985.tb00700.xSave Citation »Export Citation »E-mail Citation »

                                                      An empirical demonstration of the idea of competition for enemy-free space with data from freshwater invertebrate species.

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                                                      • MacArthur, R. H., and R. Levins. 1964. Competition, habitat selection and character displacement in a patchy environment. Proceedings of the National Academy of Sciences of the United States of America 12:197–229.

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                                                        One of the first comprehensive mathematical treatments of multispecies competition. It is a model that has provided the basis for much of the theory on competition since then.

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                                                        • MacArthur, R. H., and R. Levins. 1967. The limiting similarity, convergence and divergence of coexisting species. American Naturalist 101:377–385.

                                                          DOI: 10.1086/282505Save Citation »Export Citation »E-mail Citation »

                                                          An influential paper that attempted to provide a formal mathematical quantification of limiting similarity, the minimum amount of niche differentiation required for stable coexistence of competing species.

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                                                          • Schmitt, R. J. 1987. Indirect interactions between prey: Apparent competition, predator aggregation, and habitat segregation. Ecology 68:1887–1897.

                                                            DOI: 10.2307/1939880Save Citation »Export Citation »E-mail Citation »

                                                            One of the few experimental demonstrations of apparent competition in a natural community. Gastropod species that did not compete for common resources but did share a common group of predators exerted mutually negative interactions on one another by increasing the abundance of their shared predators.

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                                                            • Tilman, D. 1982. Resource competition and community structure. Princeton, NJ: Princeton Univ. Press.

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                                                              A comprehensive treatment of resource competition theory, based on the R* rule, that has provided the foundation for much of the later theory on competitive coexistence.

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                                                              Conceptual Syntheses

                                                              This section highlights recent conceptual syntheses that have made an important impact on the field. Foremost among these are Chesson 2000, on spatial and temporal mechanisms of competitive coexistence and Hubbell 2001 and its theory of neutral competitive coexistence. Adler, et al. 2006 synthesizes density-mediated and neutral coexistence mechanisms within the context of niche theory. Murdoch, et al. 2003 provides a comprehensive synthesis of mathematical models of competition in the context of consumer-resource interactions. Amarasekare 2003 develops a synthesis of spatial coexistence mechanisms, and Holyoak, et al. 2005 provides a compendium of theoretical and empirical papers reflecting the latest developments in spatial coexistence via metacommunity dynamics. Chesson and Kuang 2008 integrates mathematical concepts of competition and consumer-resource interactions within a common framework. Jabot and Pottier 2012 develops a common mathematical framework that integrates Grime’s and Tilman’s ideas about resource competition.

                                                              • Adler P. B., J. HilleRisLambers, and J. M. Levine. 2006. A niche for neutrality. Ecology Letters 10:95–104.

                                                                DOI: 10.1111/j.1461-0248.2006.00996.xSave Citation »Export Citation »E-mail Citation »

                                                                Synthesizes niche-based and neutral mechanisms of species coexistence within the framework of classical coexistence theory, using the ideas of stabilizing and fitness-equalizing mechanisms.

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                                                                • Amarasekare, P. 2003. Competitive coexistence in spatially structured environments: A synthesis. Ecology Letters 6:1109–1122.

                                                                  DOI: 10.1046/j.1461-0248.2003.00530.xSave Citation »Export Citation »E-mail Citation »

                                                                  Synthesizes recent theory on spatial coexistence mechanisms and develops comparative predictions that can be used to distinguish between different mechanisms.

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                                                                  • Chesson, P. 2000. Mechanisms of maintenance of species diversity. Annual Review of Ecology and Systematics 31:343–366.

                                                                    DOI: 10.1146/annurev.ecolsys.31.1.343Save Citation »Export Citation »E-mail Citation »

                                                                    An influential paper that is essential reading for those who want a rigorous and comprehensive understanding of coexistence mechanisms in spatiotemporally variable environments.

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                                                                    • Chesson, P., and J. Kuang. 2008. The interaction between predation and competition. Nature 456:235–238.

                                                                      DOI: 10.1038/nature07248Save Citation »Export Citation »E-mail Citation »

                                                                      Provides a multi-trophic perspective of species coexistence by simultaneously considering the effects of competition and predation on species coexistence.

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                                                                      • Holyoak, M., M. A. Leibold, and R. D. Holt. 2005. Metacommunities: Spatial Dynamics and Ecological Communities. Chicago: Univ. of Chicago Press.

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                                                                        A comprehensive synthesis of spatial coexistence mechanisms in metacommunities of interacting species from behavioral, ecological, and evolutionary perspectives.

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                                                                        • Hubbell, S. P. 2001. The unified neutral theory of biodiversity and biogeography. Princeton, NJ: Princeton Univ. Press.

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                                                                          An influential and controversial theory that proposes competition to be unimportant in driving species diversity. The theory proposes that coexistence results from immigration, speciation, and dispersal, thus enabling the transient coexistence of ecologically equivalent.

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                                                                          • Jabot, F., and J. Pottier. 2012. A general modelling framework for resource-ratio and CSR theories of plant community dynamics. Journal of Animal Ecology 100:1296–1302.

                                                                            DOI: 10.1111/j.1365-2745.2012.02024.xSave Citation »Export Citation »E-mail Citation »

                                                                            Uses a mathematical model to integrate Grime’s CSR and Tilman’s resource ratio hypotheses within a common conceptual framework. This framework serves to identify the conditions under which the two mechanisms can facilitate coexistence.

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                                                                            • Murdoch, W. W., C. J. Briggs, and R. M. Nisbet. 2003. Consumer-resource dynamics. Princeton, NJ: Princeton Univ. Press.

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                                                                              The definitive work on consumer-resource dynamics, with a comprehensive analysis of competition and coexistence in parasitoids and predators.

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                                                                              Mechanisms of Competitive Coexistence

                                                                              The question of what mechanisms allow competing species to coexist has absorbed theoretical and empirical ecologists for nearly two centuries. When two or more species compete for a limited resource(s), coexistence can occur via two basic classes of mechanisms. The first class of mechanisms, broadly termed “local niche partitioning,” enables coexistence via density-dependent negative feedback loops that operate within local communities in the absence of spatial or temporal variation. The second class of mechanisms enables coexistence by allowing organisms to avoid or minimize inter-specific competition in space or time. Such mechanisms rely on spatial or temporal variation in the abiotic environment and are appropriately termed “spatial niche partitioning” or “temporal niche partitioning.” This section focuses on key papers that address the question of coexistence via local niche partitioning.

                                                                              Mechanisms Independent of Environmental Variation

                                                                              This section focuses on key empirical and theoretical papers on the various mechanisms of local niche partitioning that allow competing species to coexist in the absence of environmental variation. The first set of papers focuses on Exploitative and Interference Competition for space and/or multiple resources, and the second set focuses on Coexistence via Trade-offs between different types of competition.

                                                                              Exploitative and Interference Competition

                                                                              Exploitative competition occurs when individuals have indirect negative effects on other individuals by acquiring a resource and thus depriving others of access to the resource. Interference competition occurs when individuals have direct negative effects by preventing others’ access to the resource via aggressive behaviors such as territoriality, larval competition, overgrowth, or undercutting. Tilman 1977 and Tilman 1980 laid the groundwork for R* theory and the resource-ratio theory of exploitative competition, and Vance 1984 developed the theory of coexistence when competition involves both exploitative and interference competition. Based on an important experimental study in Hanski and Kuusela 1977 on aggregation in carrion flies, Atkinson and Shorrocks 1981 developed a theory of coexistence via intra-specific aggregation, which was mathematically formalized in Ives and May 1985, Ives 1988, and Klopfer and Ives 1997.

                                                                              • Atkinson, W. D., and B. Shorrocks. 1981. Competition on a divided and ephemeral resource: A simulation model. Journal of Animal Ecology 50:461–471.

                                                                                DOI: 10.2307/4067Save Citation »Export Citation »E-mail Citation »

                                                                                The first paper to suggest that coexistence could be possible via intra-specific aggregation of competing species. Coexistence is possible because aggregation causes intra-specific competition to be stronger than inter-specific competition.

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                                                                                • Hanski, I., and S. Kuusela. 1977. An experiment on competition and diversity in a carrion fly community. Annales Zoologi Fennici 43:108–115.

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                                                                                  An experimental study of carrion flies demonstrating that intra-specific aggregation can promote coexistence.

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                                                                                  • Ives, A. R. 1988. Aggregation and the coexistence of competitors. Annales Zoologici Fennici 25:75–88.

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                                                                                    A formal mathematical model of intra-specific aggregation in competing species, whose outcomes are illustrated with data from a carrion fly community.

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                                                                                    • Ives, A. R., and R. M. May. 1985. Competition within and between species in a patchy environment: relations between microscopic and macroscopic models. Journal of Theoretical Biology 115:65–92.

                                                                                      DOI: 10.1016/S0022-5193(85)80007-2Save Citation »Export Citation »E-mail Citation »

                                                                                      A mathematical model motivated by the work of Atkinson and Shorrocks that formalizes their finding in Atkinson and Shorrocks 1981 that intra-specific aggregation promotes the coexistence of species that engage in both contest and scramble competition within local patches.

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                                                                                      • Klopfer, E. D., and A. R. Ives. 1997. Aggregation and the coexistence of competing parasitoid species. Theoretical Population Biology 52:167–178.

                                                                                        DOI: 10.1006/tpbi.1997.1335Save Citation »Export Citation »E-mail Citation »

                                                                                        Mathematical analysis of different types of aggregation (density-independent, direct density-dependent, inverse density-dependent) can facilitate the coexistence of specialist parasitoid species that attack the same host species. Interestingly, density-independent aggregation has a stronger effect on facilitating coexistence than density-dependent aggregation.

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                                                                                        • Tilman, D. 1977. Resource competition between planktonic algae: An experimental and theoretical approach. Ecology 58:338–348.

                                                                                          DOI: 10.2307/1935608Save Citation »Export Citation »E-mail Citation »

                                                                                          An empirical demonstration of the coexistence between two diatom species via the partitioning of two essential resources (phosphorous and silicate). Provided the motivation for the development of resource-ratio theory (see Tilman 1980).

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                                                                                          • Tilman, D. 1980. Resources: A graphical-mechanistic approach to competition and predation. American Naturalist 116:362–393.

                                                                                            DOI: 10.1086/283633Save Citation »Export Citation »E-mail Citation »

                                                                                            An influential paper that builds on previous empirical work to propose a coexistence mechanism involving differences between competing species in their requirement of two or more essential resources. Originally motivated by competition between plankton species, the theory has since proved to be widely applicable.

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                                                                                            • Vance, R. 1984. Interference competition and the coexistence of two competitors on a single limiting resource. Ecology 65:1349–1357.

                                                                                              DOI: 10.2307/1939115Save Citation »Export Citation »E-mail Citation »

                                                                                              A mathematical model of two species engaging in both exploitative and interference competition and the conditions under which such species can stably coexist. Coexistence occurs via a trade-off between resource exploitation ability and interference ability, which allows each species to limit itself more than it does its competitor.

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                                                                                              Coexistence via Trade-offs

                                                                                              Holt, et al. 1994 and Leibold 1996 developed theory for predicting coexistence via a trade-off between exploitative and apparent competition. Noonburg and Abrams 2005 shows that such trade-offs do not guarantee coexistence when consumers and resources experience oscillatory dynamics and when there is spatial variation in resource or consumer traits. Nowak and May 1994a, Nowak and May 1994b, and Nowak and May 1995 investigate the role of competition in the evolution of virulence in parasites and pathogens. Ojosnegros, et al. 2012 has recently shown that a trade-off between competition and colonization ability can lead to the coexistence of high-virulence and low-virulence pathogen strains.

                                                                                              • Holt, R. D., J. Grover, and D. Tilman. 1994. Simple rules for interspecific dominance in systems with exploitative and apparent competition. American Naturalist 144:741–771.

                                                                                                DOI: 10.1086/285705Save Citation »Export Citation »E-mail Citation »

                                                                                                Formulates an equivalent rule to R* for species that do not compete with one another but have mutually negative effects due to their sharing of a common predator (P* rule for apparent competition). It analyzes models in which species engage in both exploitative and apparent competition and coexistence is determined by the balance between R* and P* rules.

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                                                                                                • Leibold, M. A. 1996. A graphical model of keystone predators in foodwebs: Trophic regulation of abundance, incidence and diversity patterns in communities. American Naturalist 147:784–812.

                                                                                                  DOI: 10.1086/285879Save Citation »Export Citation »E-mail Citation »

                                                                                                  A graphical model that investigates coexistence of two species that share a common resource and a shared natural enemy. The key insight is that coexistence occurs via an inter-specific trade-off between competitive ability and susceptibility to predation, i.e., one species has a lower R* and the other species has a higher P*.

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                                                                                                  • Noonburg, E., and P. A. Abrams. 2005. Transient dynamics and prey species coexistence with shared resources and predator. American Naturalist 165:322–335.

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                                                                                                    Shows that a trade-off between competitive ability and susceptibility to predation does not guarantee coexistence when communities exhibit fluctuating local dynamics and/or experience spatial variation in resource or predator traits.

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                                                                                                    • Nowak, M. A., and R. M. May. 1994a. Superinfection and the evolution of parasite virulence. Proceedings of the Royal Society B: Biological Sciences 255:81–89.

                                                                                                      DOI: 10.1098/rspb.1994.0012Save Citation »Export Citation »E-mail Citation »

                                                                                                      Challenges the conventional wisdom that parasites should evolve intermediate levels of virulence by showing that selection can lead to the evolution of high virulence in the face of superinfection (the reinfection of an already infected host by another parasite, a form of intra-specific competition) and the resulting competition between parasites within hosts.

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                                                                                                      • Nowak, M. A., and R. M. May. 1994b. Superinfection, metapopulation dynamics and the evolution of diversity. Journal of Theoretical Biology 170:95–114.

                                                                                                        DOI: 10.1006/jtbi.1994.1171Save Citation »Export Citation »E-mail Citation »

                                                                                                        Adapts the patch occupancy framework to analyze the maintenance of host-parasite diversity via trade-offs between competitive ability, colonization ability, and extinction rates of hosts and parasites.

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                                                                                                        • Nowak, M. A., and R. M. May. 1995. Coinfection and the evolution of parasite virulence. Proceedings of the Royal Society B-Biological Sciences 261:209–215.

                                                                                                          DOI: 10.1098/rspb.1995.0138Save Citation »Export Citation »E-mail Citation »

                                                                                                          Analyzes the evolution of virulence of parasites when a given host can be parasitized by different types of parasitic strains (a form of inter-specific competition). It shows that when there is co-infection, virulence evolves to a level that maintains the parasite’s basic reproductive rate above unity.

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                                                                                                          • Ojosnegros, S., E. Delgado-Eckert, and N. Beerenwinkel. 2012. Competition-colonization trade-off promotes coexistence of low-virulence viral strains. Journal of the Royal Society Interface 9:2244–2254.

                                                                                                            DOI: 10.1098/rsif.2012.0160Save Citation »Export Citation »E-mail Citation »

                                                                                                            Investigates the evolution of virulence in RNA viruses by introducing a competition-colonization trade-off to a standard model of within-host viral infection. The key result is that a trade-off allows the coexistence of low-virulent inferior competitors with high-virulent superior competitors.

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                                                                                                            Mechanisms Dependent on Environmental Variation

                                                                                                            Temporal variation enables coexistence by allowing species to differ in terms of when they use a limiting resource, and spatial variation enables coexistence by allowing species to differ in terms of where they use a limiting resource. In both cases, coexistence results because intra-specific competition is concentrated, in time or space, relative to inter-specific competition. The next two sections highlight key theoretical and empirical papers that deal with variation-dependent coexistence mechanisms.

                                                                                                            Temporal Niche Partitioning: Nonlinear Competitive Responses

                                                                                                            Most animal species exhibit nonlinear functional responses (the relationship between per capita resource consumption and resource abundance), which cause the species’ per capita growth rates to depend on resource abundance in a nonlinear manner. Hutchinson 1961 first suggested the possibility that nonlinear competitive responses to temporal variation could allow multiple species to coexist. Hutchinson’s ideas were later formalized in Armstrong and McGehee 1980, which is an important paper and remains a classic. Armstrong and McGehee showed that when resource abundance fluctuates over time, and species that compete for the resource differ in the degree of nonlinearity in their functional responses, stable coexistence is possible if the species with the more nonlinear response is more disadvantaged, when abundant, by resource fluctuations than the species with the less nonlinear response. Huisman and Weissing 1999 provides both a contemporary theoretical framework and empirical verification of this coexistence mechanism. Kang and Chesson 2010 builds on the idea of nonlinear competitive responses to derive conditions for permanence.

                                                                                                            • Armstrong, R. A., and R. McGehee. 1980. Competitive exclusion. American Naturalist 115:151–170.

                                                                                                              DOI: 10.1086/283553Save Citation »Export Citation »E-mail Citation »

                                                                                                              A classic paper that provides a rigorous mathematical analysis of coexistence via nonlinear competitive responses. A must-read for anyone interested in understanding how species-specific differences in resource acquisition can facilitate coexistence in a variable environment.

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                                                                                                              • Huisman, J., F. J. Weissing. 1999. Biodiversity of plankton by species oscillations and chaos. Nature 402:407–410.

                                                                                                                DOI: 10.1038/46540Save Citation »Export Citation »E-mail Citation »

                                                                                                                Using consumer-resource models with saturating functional responses, these authors show that nonlinear competitive responses to a fluctuating environment can allow the coexistence of large numbers of species when they compete for multiple resources. Model predictions are verified with data on plankton communities.

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                                                                                                                • Hutchinson, G. E. 1961. Paradox of the plankton. American Naturalist 95:137–145.

                                                                                                                  DOI: 10.1086/282171Save Citation »Export Citation »E-mail Citation »

                                                                                                                  In this classic paper, Hutchinson posed the question: what mechanisms would enable large numbers of plankton species that share the same resource to coexist in a seemingly homogeneous environment? He posited that temporal environmental variation, particularly seasonal variation, should enable coexistence by favoring different species at different times. Hutchinson’s verbal arguments have since been formalized mathematically and also demonstrated empirically (see below).

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                                                                                                                  • Kang, Y., and P. Chesson. 2010. Relative nonlinearity and permanence. Theoretical Population Biology 78:26–35.

                                                                                                                    DOI: 10.1016/j.tpb.2010.04.002Save Citation »Export Citation »E-mail Citation »

                                                                                                                    Builds on the concept of relative nonlinearity to develop rigorous conditions for permanence (long-term coexistence under point or nonpoint attractors).

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                                                                                                                    Temporal Niche Partitioning: Storage Effect

                                                                                                                    The storage effect occurs when competing species differ in their responses to abiotic environmental variation, which modify the nature of competitive interactions between species. Intra-specific competition is the strongest when a species is favored by the environment, and inter-specific competition is the strongest when a species’ competitors are favored by the environment. Chesson and Warner 1981 developed the first mathematical model of the storage effect, and Warner and Chesson 1985 provides the first field test of the phenomenon. Chesson 1986 and Chesson and Grubb 1990 give a clear summary of the key principles underlying the storage effect. The influential Chesson and Huntly 1998 develops a theoretical framework for coexistence in harsh environments, refuting the conventional wisdom that disturbances can promote coexistence. Chesson 1994 generalizes the storage effect and other coexistence mechanisms dependent on temporal variation to multiple species. Cáceres 1997 provides the first empirical quantification of the storage effect, and Angert, et al. 2009 highlights the role of functional trade-offs in enabling coexistence via the storage effect.

                                                                                                                    • Angert, A., T. Huxman, and P. Chesson. 2009. Functional tradeoffs determine species coexistence via the storage effect. Proceedings of the National Academy of Sciences of the United States of America 106:11641–11645.

                                                                                                                      DOI: 10.1073/pnas.0904512106Save Citation »Export Citation »E-mail Citation »

                                                                                                                      Illustrates the role of trade-offs between functional traits in mediating coexistence via the storage effect.

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                                                                                                                      • Cáceres, C. E. 1997. Temporal variation, dormancy, and coexistence: A field test of the storage effect. Proceedings of the National Academy of Sciences of the United States of America 94:9171–9175.

                                                                                                                        DOI: 10.1073/pnas.94.17.9171Save Citation »Export Citation »E-mail Citation »

                                                                                                                        The first empirical quantification of the storage effect as a mechanism contributing to species coexistence in a natural community.

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                                                                                                                        • Chesson, P. 1986. Environmental variation and the coexistence of species. In Community ecology. Edited by J. Diamond and T. Case, 240–256. New York: Harper and Row.

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                                                                                                                          A lucid presentation of the key ideas behind the storage effect, one of the principal mechanisms by which competing species can coexist in temporally variable environments.

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                                                                                                                          • Chesson, P. 1994. Mulitspecies coexistence in variable environments. Theoretical Population Biology 45:227–276.

                                                                                                                            DOI: 10.1006/tpbi.1994.1013Save Citation »Export Citation »E-mail Citation »

                                                                                                                            An analysis of how coexistence mechanisms dependent on environmental variation generalize to multiple species.

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                                                                                                                            • Chesson, P. L., and P. J. Grubb. 1990. Geometry, heterogeneity and competition in variable environments. Philosophical Transactions of the Royal Society of London Series B: Biological Sciences 330:165–173.

                                                                                                                              DOI: 10.1098/rstb.1990.0190Save Citation »Export Citation »E-mail Citation »

                                                                                                                              Provides a geometric analysis of how environmental fluctuations can promote coexistence. The important insight is the demonstration that when growth rates of competing species have a subadditive geometric form, species at low densities have a growth rate advantage, on average, over species at high densities.

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                                                                                                                              • Chesson, P., and N. Huntly. 1998. The role of harsh and fluctuating conditions in the dynamics of ecological communities. American Naturalist 150:519–553.

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                                                                                                                                An important paper that provides a rigorous mathematical analysis to refute the common misconception that harsh and fluctuating environmental conditions reduce competition and allow coexistence and to show that coexistence is possible when these environmental factors create opportunities for spatial or temporal niche partitioning.

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                                                                                                                                • Chesson, P. L., and R. R. Warner. 1981. Environmental variability promotes coexistence in lottery-competitive systems. American Naturalist 117:923–943.

                                                                                                                                  DOI: 10.1086/283778Save Citation »Export Citation »E-mail Citation »

                                                                                                                                  A model of how competition for space in a lottery system (i.e., whoever gets there first wins) can allow coexistence in spatially variable environments in species with overlapping generations (the storage effect). A keystone paper that laid the foundation for all subsequent theoretical developments on competitive coexistence in variable environments.

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                                                                                                                                  • Warner, R. R., and P. L. Chesson. 1985. Coexistence mediated by recruitment fluctuations: A field guide to the storage effect. American Naturalist 125:769–787.

                                                                                                                                    DOI: 10.1086/284379Save Citation »Export Citation »E-mail Citation »

                                                                                                                                    A test of the hypothesis (formulated in Chesson and Warner 1981) that fluctuations in birth rates can facilitate the coexistence of long-lived organisms with data from coral- reef fish communities. A first test of the storage effect in a natural community.

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                                                                                                                                    Spatial Niche Partitioning: Trade-offs

                                                                                                                                    Hastings 1980 provided the first mathematical model of spatial competitive coexistence via a trade-off between competitive ability and dispersal ability. Nee and May 1992 and Tilman, et al. 1994 extend Hastings’s model to include effects of habitat destruction on species diversity when species coexist via competition-colonization trade-offs. Comins and Noble 1985 shows that trade-off coexistence is not possible when species engage in preemptive competition, and Yu and Wilson 2001 shows that coexistence of such species is possible if there is spatial variation in patch density. Shurin 2000 and Shurin and Allen 2001 provide theoretical and empirical evidence of spatial coexistence via a trade-off between competitive ability and susceptibility to predation. Kondoh 2003 demonstrates that species that differ in their competitive ability but have similar susceptibilities to a common predator can coexist if the superior competitor is more spatially aggregated and hence prone to more predator attacks.

                                                                                                                                    • Comins, H. N., and I. R. Noble. 1985. Dispersal, variability, and transient niches: Species coexistence in a uniformly variable environment. American Naturalist 126:706–723.

                                                                                                                                      DOI: 10.1086/284448Save Citation »Export Citation »E-mail Citation »

                                                                                                                                      A mathematical analysis of competitive coexistence in patchy environments when species engage in preemptive (lottery competition).

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                                                                                                                                      • Hastings, A. 1980. Disturbance, coexistence, history and competition for space. Theoretical Population Biology 18:363–373.

                                                                                                                                        DOI: 10.1016/0040-5809(80)90059-3Save Citation »Export Citation »E-mail Citation »

                                                                                                                                        The first mathematical demonstration of coexistence via a trade-off between competitive ability and colonization ability using a patch occupancy model. In patchy environments, competitively superior species displace competitively inferior species when they co-occur, but inferior competitors that are superior dispersers can avoid regional exclusion because they are able to reach patches that superior competitors, because of the their limited dispersal ability, cannot colonize.

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                                                                                                                                        • Kondoh, M. 2003. High reproductive rates result in high predation risks: A mechanism promoting the coexistence of competing prey in spatially structured populations. American Naturalist 161:299–309.

                                                                                                                                          DOI: 10.1086/345939Save Citation »Export Citation »E-mail Citation »

                                                                                                                                          Demonstrates that a trade-off between competitive ability and susceptibility to predator attack (one that is typically assumed to arise from life-history differences) can also arise through species’ responses to spatial variation and allow the coexistence of species that exhibit similar levels of predator susceptibility.

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                                                                                                                                          • Nee, S., and R. M. May. 1992. Dynamics of metapopulations: Habitat destruction and competitive coexistence. Journal of Animal Ecology 61:37–40.

                                                                                                                                            DOI: 10.2307/5506Save Citation »Export Citation »E-mail Citation »

                                                                                                                                            An extension of the patch occupancy models to investigate the effects of habitat destruction on the coexistence of species via a trade-off between competitive ability and colonization ability. Provides a mathematical analysis to show that species with similar competitive abilities can persist if they differ in their mortality rates.

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                                                                                                                                            • Shurin, J. B. 2000. Dispersal limitation, invasion resistance, and the structure of pond zooplankton communities. Ecology 81:3074–3086.

                                                                                                                                              DOI: 10.1890/0012-9658(2000)081[3074:DLIRAT]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

                                                                                                                                              This is an empirical study that investigates predator and dispersal effects on zooplankton diversity. It found that fish and insect predators increased the extinction of large-bodied zooplankton (putative superior competitors) and facilitated invasion by inferior competitors from the regional pool, thus providing support to the hypothesis that a trade-off between competitive ability and susceptibility to predation can promote competitive coexistence in patchy environments.

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                                                                                                                                              • Shurin, J. B., and E. G. Allen. 2001. Effects of competition, predation and dispersal on species richness at local and regional scales. American Naturalist 158:624–637.

                                                                                                                                                DOI: 10.1086/323589Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                Demonstrates that when a trade-off between competitive ability and susceptibility to a common predator allows local coexistence of consumers that share a common resource and a predator, extinction-colonization dynamics can significantly enhance consumer coexistence at the metacommunity scale. Model predictions are supported by data on plankton and fish communities.

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                                                                                                                                                • Tilman, D., R. M. May, C. Lehman, and M. Novak. 1994. Habitat destruction and the extinction debt. Nature 371:65–66.

                                                                                                                                                  DOI: 10.1038/371065a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                  A multispecies version of Hastings 1980 on competition-colonization trade-offs. Investigates the effects of habitat destruction and finds that, paradoxically, habitat destruction is more detrimental to superior competitors, causing them to go extinct before inferior competitors. Extinctions occur many generations after habitat destruction has occurred and hence incurs an “extinction debt.”

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                                                                                                                                                  • Yu, D. W., and H. B. Wilson. 2001. The competition-colonization trade-off is dead; long live the competition-colonization trade-off. American Naturalist 158:49–63.

                                                                                                                                                    DOI: 10.1086/320865Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                    Uses a mathematical model to provide a spatial coexistence mechanism for species engaging in preemptive (lottery) competition. Coexistence of such species is possible if patch density varies spatially such that it becomes a niche axis.

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                                                                                                                                                    Spatial Niche Partitioning: Spatial Nonlinearity and Spatial Storage Effect

                                                                                                                                                    Chesson 1985 investigates mechanisms of coexistence in spatiotemporally variable environments, and Chesson 2000 develops a general theoretical framework for spatial competitive coexistence. Snyder and Chesson 2005 investigates the role of spatial scale in determining the relative importance of spatial nonlinearity and the storage effect. Wilson and Abrams 2006 shows that dispersal can enable the coexistence of species that exhibit nonlinear competitive responses, provided that dynamics are spatially asynchronous.

                                                                                                                                                    • Chesson, P. L. 1985. Coexistence of competitors in spatially and temporally varying environments: A look at the combined effects of different sorts of variability. Theoretical Population Biology 28:263–287.

                                                                                                                                                      DOI: 10.1016/0040-5809(85)90030-9Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                      Investigates the role of different types of environmental variability in promoting coexistence via a storage effect.

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                                                                                                                                                      • Chesson, P. 2000. General theory of competitive coexistence in spatially-varying environments. Theoretical Population Biology 58:211–237.

                                                                                                                                                        DOI: 10.1006/tpbi.2000.1486Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                        A general model of competitive and apparent competitive interactions to elucidate the conditions under which coexistence can occur in spatially varying environments.

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                                                                                                                                                        • Snyder, R. E., and P. Chesson. 2005. How the spatial scales of dispersal, competition, and environmental heterogeneity interact to affect coexistence. American Naturalist 164:633–650.

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                                                                                                                                                          Develops a mathematical framework to determine how the spatial scales of competition, dispersal, and heterogeneity affect the relative importance of the three spatial coexistence mechanisms: storage effect, relative nonlinearity, and growth-density covariance.

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                                                                                                                                                          • Wilson, W., and P. A. Abrams. 2006. Coexistence of cycling, dispersing consumer species: Armstrong and McGehee in space. American Naturalist 165:193–205.

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                                                                                                                                                            Extends the idea of coexistence via nonlinear competitive responses, initially developed in Armstrong and McGehee 1980 (cited under Temporal Niche Partitioning: Nonlinear Competitive Responses) to include spatial structure to show that dispersal can enhance or constrain coexistence depending on the degree of temporal synchrony in population dynamics.

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                                                                                                                                                            Exploitative Competition and Source-Sink Dynamics

                                                                                                                                                            Amarasekare and Nisbet 2001 developed one of the first mathematical models of source-sink dynamics of species engaging in exploitative competition. Mouquet and Loreau 2002 investigates the role of source-sink dynamics in generating diversity and limiting similarity when species engage in lottery competition. Abrams and Wilson 2004 and Namba and Hashimoto 2004 develop models of consumer-resource interactions to show that dispersal can enable species with higher R* values to coexist with species with lower R* values. Amarasekare, et al. 2004 provides a comparative mathematical analysis of source-sink dynamics and competition-colonization trade-offs to identify the conditions under which multiple spatial mechanisms can enable competitive coexistence. Codeco and Grover 2001 and Fox 2007 provide empirical tests of source-sink dynamics in enabling spatial coexistence in microbial metacommunities.

                                                                                                                                                            • Abrams, P., and W. G. Wilson. 2004. Coexistence of competitors in metacommunities due to spatial variation in resource growth rates: Does R* predict the outcome of competition? Ecology Letters 7:929–940.

                                                                                                                                                              DOI: 10.1111/j.1461-0248.2004.00644.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                              Uses a mathematical model of consumers and resources to show that when resource traits vary but consumer traits do not, a species with a higher R* value (an inferior competitor) can coexist with a species with a lower R* value (a superior competitor) if the latter has a higher emigration rate from localities of greater resource productivity such that the inferior competitor can invade such habitats when rare.

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                                                                                                                                                              • Amarasekare, P., M. Hoopes, N. Mouquet, and M. Holyoak. 2004. Mechanisms of coexistence in competitive metacommunities. American Naturalist 164:310–326.

                                                                                                                                                                DOI: 10.1086/422858Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                Develops a mathematical framework that integrates spatial coexistence mechanisms based on competition-colonization trade-offs and source-sink dynamics to develop comparative predictions about the conditions under which each mechanism is likely to prevail in metacommunities of competing species.

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                                                                                                                                                                • Amarasekare, P., and R. M. Nisbet. 2001. Spatial heterogeneity, source-sink dynamics and the local coexistence of competing species. American Naturalist 158:572–584.

                                                                                                                                                                  DOI: 10.1086/323586Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                  One of the first mathematical studies to demonstrate the coexistence of competing species via source-sink dynamics in patchy environments.

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                                                                                                                                                                  • Fox, J. W. 2007. Testing the mechanisms by which source-sink dynamics alter competitive outcomes in a model system. American Naturalist 170:396–408.

                                                                                                                                                                    DOI: 10.1086/519855Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                    One of the first experimental studies of source-sink dynamics in competitive communities, which uses laboratory microcosms to test the role of source-sink dynamics in allowing competitive coexistence.

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                                                                                                                                                                    • Codeco, C. T., and J. P. Grover. 2001. Competition along a spatial gradient of resource supply: A microbial experimental model. American Naturalist 157:300–315.

                                                                                                                                                                      DOI: 10.1086/319195Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                      An experimental study of microbial communities demonstrating competitive coexistence via source-sink dynamics.

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                                                                                                                                                                      • Mouquet, N, and M. Loreau. 2002. Coexistence in metacommunities: The regional similarity hypothesis. American Naturalist 159:420–426.

                                                                                                                                                                        DOI: 10.1086/338996Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                        Analyzes a multispecies metacommunity of species engaging in lottery competition and derives conditions for coexistence and limiting similarity at the regional scale.

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                                                                                                                                                                        • Namba, T., and C. Hashimoto. 2004. Dispersal-mediated coexistence of competing predators. Theoretical Population Biology 66:53–70.

                                                                                                                                                                          DOI: 10.1016/j.tpb.2004.03.003Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                          Obtains the same qualitative results as Abrams and Wilson 2004 in a model with Type II functional responses, illustrating the robustness of the coexistence mechanism to the functional form of resource use.

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                                                                                                                                                                          Spatial Coexistence of Species at Multiple Trophic Levels

                                                                                                                                                                          McCann, et al. 2005 demonstrates how mobile consumers can couple foodwebs in space, thus increasing both foodweb persistence and diversity. Amarasekare 2007, Amarasekare 2008, and Amarasekare 2010 develop models of community modules in which species engage in both competition and predation, and illustrates the role of nonrandom dispersal strategies in enabling spatial coexistence.

                                                                                                                                                                          • Amarasekare, P. 2007. Spatial dynamics of communities with intraguild predation: The role of dispersal strategies. American Naturalist 170:819–831.

                                                                                                                                                                            DOI: 10.1086/522837Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                            Provides a mathematical analysis of nonrandom dispersal strategies in resource-consumer metacommunities. It shows that dispersal asymmetries between species at different trophic levels can generate “keystone dispersers,” species whose dispersal can have disproportionately large effect on foodweb persistence and diversity.

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                                                                                                                                                                            • Amarasekare, P. 2008. Spatial dynamics of keystone predation. Journal of Animal Ecology 77:1306–1315.

                                                                                                                                                                              DOI: 10.1111/j.1365-2656.2008.01439.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                              Develops a four-species community module with dispersal at consumer and predator trophic levels to elucidate the conditions under which spatial coexistence is possible in consumer species that share a common resource and predator.

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                                                                                                                                                                              • Amarasekare, P. 2010. Effect of non-random dispersal strategies on spatial coexistence mechanisms. Journal of Animal Ecology 79:282–293.

                                                                                                                                                                                DOI: 10.1111/j.1365-2656.2009.01607.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                Provides a mathematical framework for elucidating the conditions under which nonrandom dispersal mechanisms allow coexistence of species engaged in exploitative and apparent competition.

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                                                                                                                                                                                • McCann, K. S., R. B. Rasmussen, and J. Umbanhowar. 2005. The dynamics of spatially coupled foodwebs. Ecology Letters 8:513–523.

                                                                                                                                                                                  DOI: 10.1111/j.1461-0248.2005.00742.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                  Provides an alternative spatial coexistence mechanism to source-sink and extinction-colonization dynamics. It argues that movement of consumers that are more mobile than their resources can couple foodweb modules in different localities, thus increasing both foodweb persistence and consumer-resource diversity.

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                                                                                                                                                                                  Apparent Competition and Source-Sink Dynamics

                                                                                                                                                                                  Holt 1984 elucidates the role of dispersal in mediating coexistence in species engaging in apparent competition. Bonsall and Hassell 2000 shows that when species engaging in apparent competition exhibit oscillatory dynamics, differential dispersal abilities of superior and inferior apparent competitors can lead to coexistence. King and Hastings 2003 demonstrates that coexistence of apparent competitors is possible if species form spatial clusters with emigration and immigration between clusters.

                                                                                                                                                                                  • Bonsall, M. B, and M. P. Hassell. 2000. The effects of metapopulation structure on indirect interactions in host-parasitoid assemblages. Proceedings of the Royal Society B: Biological Sciences 267:2207–2212.

                                                                                                                                                                                    DOI: 10.1098/rspb.2000.1270Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                    Uses coupled map lattice models to show that when the apparent competitive interaction between two insect hosts that share a common parasitoid exhibits divergent oscillations, limited mobility of the inferior host results in the superior host and the parasitoid having a high degree of spatial overlap and the inferior host and the parasitoid having minimal overlap, thus leading to three-species coexistence.

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                                                                                                                                                                                    • Holt, R. D. 1984. Spatial heterogeneity, indirect interactions, and coexistence of prey species. American Naturalist 124:377–406.

                                                                                                                                                                                      DOI: 10.1086/284280Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                      Illustrates how effects of dispersal on coexistence depends crucially on the type of competitive interaction. Prey species that share a predator do not experience apparent competition when they occupy different habitat types and the predator is immobile. However, predator dispersal between habitat types can create apparent competition and cause the inferior apparent competitor’s exclusion from the entire metacommunity.

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                                                                                                                                                                                      • King, A. A., and A. Hastings. 2003. Spatial mechanisms for coexistence of species sharing a common natural enemy. Theoretical Population Biology 64:431–438.

                                                                                                                                                                                        DOI: 10.1016/S0040-5809(03)00100-XSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                        This follow-up paper uses explicit within-patch dynamics and global dispersal and shows that coexistence of apparent competitors does not require spatial patterning but rather the formation of clusters, collections of patches that exhibit identical dynamics. Within a given cluster, the inferior apparent competitor could be driven to low densities but is rescued from extinction via immigration between clusters that exhibit asynchronous dynamics.

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                                                                                                                                                                                        Evolutionary Consequences of Competition

                                                                                                                                                                                        Competition does not only affect the ecological dynamics (changes in per capita growth rates and abundances) but also provides the biotic selective environment for the evolution of life history and resource acquisition traits, character displacement, and speciation. The next three sections highlight theoretical and empirical papers that investigate the evolutionary consequences of competition.

                                                                                                                                                                                        Conceptual Syntheses

                                                                                                                                                                                        Cody and Diamond 1985 contains a series of influential articles on the role of competition in driving the evolution of species within communities. Abrams 1990 gives an in-depth discussion of the ecological and evolutionary consequences of competition. Grether, et al. 2009 synthesizes the empirical literature and provides new theory on the role of inter-specific competition in the evolution of character displacement.

                                                                                                                                                                                        • Abrams, P. A. 1990. Ecological vs. evolutionary consequences of competition. Oikos 57:147–151.

                                                                                                                                                                                          DOI: 10.2307/3565752Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                          An influential early paper that raises the important point that ecological and evolutionary consequences of competition need not be similar and may in fact be opposite.

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                                                                                                                                                                                          • Cody, M. L., and J. M. Diamond. 1985. Ecology and evolution of communities. Cambridge, UK: Cambridge Univ. Press.

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                                                                                                                                                                                            Contains eighteen original articles by leaders in the fields of ecology and evolution, with a major section on the role of competition in driving the ecology and evolution of communities.

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                                                                                                                                                                                            • Grether, G. F., N. Losin, C. Anderson, and K. Okamoto. 2009. The role of interspecific interference competition in character displacement. Biological Reviews 84:617–635.

                                                                                                                                                                                              DOI: 10.1111/j.1469-185X.2009.00089.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                              Combines data from the literature with a mathematical model to show that interference competition can be a strong selective force in the evolution of character displacement.

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                                                                                                                                                                                              Character Displacement

                                                                                                                                                                                              Character displacement is one of the major evolutionary consequences of competition. Schluter, et al. 1985 and Schluter and McPhail 1992 provide empirical evidence of character displacement in the Darwin’s finches. Taper and Case 1985 develops a quantitative genetic framework for predicting character displacement via coevolution in competing species. Rummel and Roughgarden 1985 develops the idea of taxon cycles based on empirical studies of Anolis lizards in the Caribbean. Saloneimi 1993 provides empirical evidence of character displacement in snails, and Svanback, et al. 2008 illustrates the role of competition in driving multispecies polymorphisms in fish. Fox and Vasseur 2008 and Vasseur and Fox 2011 provide a counter-example of competition leading to character convergence.

                                                                                                                                                                                              • Fox, J., and D. A. Vasseur. 2008. Character convergence under competition for essential resources. American Naturalist 172:667–680.

                                                                                                                                                                                                DOI: 10.1086/591689Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                Goes against the grain in showing that competition for essential resources can lead to character convergence rather than divergence.

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                                                                                                                                                                                                • Rummel, J. D., and J. Roughgarden. 1985. The theory of faunal build-up for competition communities. Evolution 39:1009–1033.

                                                                                                                                                                                                  DOI: 10.2307/2408731Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                  Uses empirical studies of Anolis lizards in the Caribbean to suggest that asymmetric competition between species can lead to taxon cycles on an evolutionary time scale. An important idea that spawned a great deal of theoretical and empirical interest.

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                                                                                                                                                                                                  • Saloneimi, I. 1993. An environmental explanation for the character displacement pattern in Hydrobia snails. Oikos 67:75–80.

                                                                                                                                                                                                    DOI: 10.2307/3545097Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                    An empirical study of character displacement due to resource competition in mud snails where species living apart consume similar-sized resources but species that co-occur show niche differentiation in the size of the food particles they consume.

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                                                                                                                                                                                                    • Schluter, D., and J. D. McPhail. 1992. Ecological character displacement and speciation in three-spine sticklebacks. American Naturalist 140:85–108.

                                                                                                                                                                                                      DOI: 10.1086/285404Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                      An empirical example of ecological character displacement (differentiation in morphological traits associated with resource use) in three-spine sticklebacks in freshwater lakes of British Columbia, allowing coexistence of species pairs that co-occur in some of the lakes.

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                                                                                                                                                                                                      • Schluter, D., T. D. Price, and P. R. Grant. 1985. Ecological character displacement in Darwin’s finches. American Naturalist 227:1056–1059.

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                                                                                                                                                                                                        Presents strong empirical evidence for character displacement driven by resource competition in Darwin’s finches.

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                                                                                                                                                                                                        • Svanback, R. R., P. Eklöv, R. Fransson, and K. Holmgren. 2008. Intra-specific competition drives multiple species trophic polymorphism in fish communities. Oikos 117:114–124.

                                                                                                                                                                                                          DOI: 10.1111/j.2007.0030-1299.16267.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                          An empirical study illustrating the role of competition in driving multispecies polymorphisms.

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                                                                                                                                                                                                          • Taper, M. L., and T. J. Case. 1985. Quantitative genetic models for the coevolution of character displacement. Ecology 66:355–371.

                                                                                                                                                                                                            DOI: 10.2307/1940385Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                            Uses quantitative genetic models to investigate the evolution of character displacement driven by inter-specific competition for resources. Model predictions about intra- and inter-specific niche and character separation are consistent with data from the literature.

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                                                                                                                                                                                                            • Vasseur, D. A., and J. Fox. 2011. Adaptive dynamics of competition for nutritionally complementary resources: Character convergence, displacement, and parallelism. American Naturalist 178:501–514.

                                                                                                                                                                                                              DOI: 10.1086/661896Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                              Investigates the ecological and evolutionary consequences of competition for complementary resources. It finds that, contrary to previous results, coadaptation of competing consumers always leads to stable coexistence.

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                                                                                                                                                                                                              Sympatric Speciation

                                                                                                                                                                                                              Competition, if it leads to sufficient amounts of divergence, can lead to sympatric speciation. Seger 1985 provides a mathematical analysis of the mechanisms by which resource competition leads to sympatric speciation. Schluter 1994 provides experimental evidence of competition as a selective force underlying adaptive radiations. Doebeli 1996 develops a quantitative genetic model for competition-driven sympatric speciation, while Kisdi 1999 and Doebeli and Dieckmann 2000 use the technique of adaptive dynamics to investigate the conditions under which competition can lead to sympatric speciation. Day 2000 investigates how spatial resource heterogeneity influences selection exerted on consumers that compete for resources.

                                                                                                                                                                                                              • Day, T. 2000. Competition and the effect of spatial resource heterogeneity on evolutionary diversification. American Naturalist 155:790–803.

                                                                                                                                                                                                                DOI: 10.1086/303356Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                Presents a mathematical model investigating how spatial heterogeneity in resources influences selection arising from resource use by consumers. It determines the conditions under which disruptive selection can lead to character displacement and hence polymorphisms. Also finds that heterogeneity can both enhance and suppress such divergence.

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                                                                                                                                                                                                                • Doebeli, M. 1996. A quantitative genetic competition model for sympatric speciation. Journal of Evolutionary Biology 9:893–909.

                                                                                                                                                                                                                  DOI: 10.1046/j.1420-9101.1996.9060893.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                  Combines quantitative genetic models with models of inter-specific competition to predict the conditions under which sympatric speciation could occur via character displacement.

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                                                                                                                                                                                                                  • Doebeli, M., and U. Dieckmann. 2000. Evolutionary branching and sympatric speciation caused by different types of ecological interactions. American Naturalist 156:77–101.

                                                                                                                                                                                                                    DOI: 10.1086/303417Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                    Uses adaptive dynamics to investigate the role of competition and other ecological interactions as agents of disruptive selection, leading to character displacement and sympatric speciation.

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                                                                                                                                                                                                                    • Kisdi, E. 1999. Evolutionary branching under asymmetric competition. Journal of Theoretical Biology 197:149–162.

                                                                                                                                                                                                                      DOI: 10.1006/jtbi.1998.0864Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                      Uses the technique of adaptive dynamics to investigate how asymmetric competition could give rise to evolutionary branching driven by character displacement.

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                                                                                                                                                                                                                      • Schluter, D. 1994. Experimental evidence that competition promotes divergence in adaptive radiation. Science 266:798–801.

                                                                                                                                                                                                                        DOI: 10.1126/science.266.5186.798Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                        Illustrates the role of competition as an agent of selection in driving adaptive radiations.

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                                                                                                                                                                                                                        • Seger, J. 1985. Intraspecific resource competition as a cause of sympatric speciation. In Evolution: Essays in honour of John Maynard Smith. Edited by P. J. Greenwood, P. H. Harvey, and M. Slatkin, 43–53. Cambridge, UK: Cambridge Univ. Press.

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                                                                                                                                                                                                                          An analysis of the mechanisms by which resource competition could drive sympatric speciation.

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                                                                                                                                                                                                                          Competition as an Agent of Selection

                                                                                                                                                                                                                          Ayala 1969 provides some of the first empirical evidence of competition selective factor driving the evolution of phenotypic traits. Pease 1984 developed one of the first mathematical models of eco-evolutionary dynamics to show that evolution can lead to a reversal of competitive dominance. The recent surge of interest in the role of intra-specific variation in driving phenotypic trait evolution has spawned new theoretical studies on how intra-specific variation mediates the coexistence of species that engage in resource competition and apparent competition. Schreiber, et al. 2011 combines quantitative genetics with models of population dynamics to investigate the coexistence of apparent competitors, and Vasseur, et al. 2011 uses the same approach to illustrate how competition-driven selection and the resulting eco-evolutionary feedbacks allow the coexistence of species that engage in resource competition. Using the same ideas in a different vein, Read, et al. 2011 shows how the completion of drug treatments by patients gives a competitive advantage to drug-resistant pathogen strains, thus making it more difficult to recover from a disease.

                                                                                                                                                                                                                          • Ayala, F. J. 1969. Evolution of Fitness IV: Genetic evolution of inter-specific competitive ability in Drosophila. Genetics 61:737–747.

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                                                                                                                                                                                                                            One of the first experimental studies demonstrating the role of inter-specific competition as an agent of selection. In the presence of a second species (Drosophila nebulosa), D. serrata exhibited an increase in competitive ability consistent with evolution due to competition-mediated selection.

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                                                                                                                                                                                                                            • Pease, C. M. 1984. On the evolutionary reversal of competitive dominance. Evolution 38:1099–1115.

                                                                                                                                                                                                                              DOI: 10.2307/2408443Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                              A mathematical analysis illustrating that evolution can lead to the reversal of competitive dominance by species that engage in resource competition.

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                                                                                                                                                                                                                              • Read, A. F., T. Day, and S. Huijben. 2011. The evolution of drug resistance and the curious orthodoxy of aggressive chemotherapy. Proceedings of the National Academy of Sciences of the United States of America 108:10871–10877.

                                                                                                                                                                                                                                DOI: 10.1073/pnas.1100299108Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                                Investigates the evolution of drug resistance in pathogens in the context of within-host pathogen evolution. It shows that the medical orthodoxy of having patients complete drug treatment regimes may have the undesirable consequence of maximizing the evolutionary advantage of drug-resistant pathogens.

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                                                                                                                                                                                                                                • Schreiber, S. J., R. Burger, and D. I. Bolnick. 2011. The community effects of phenotypic and genetic variation within a predator population. Ecology 92:1582–1593.

                                                                                                                                                                                                                                  DOI: 10.1890/10-2071.1Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                                  Uses a quantitative genetics framework to investigate how phenotypic variation in a predator species influences apparent competition between its prey species. Contrary to purely ecological models in which apparent competitors have mutually negative effects on one another, intra-specific variation in the predator can not only reduce these negative effects and facilitate coexistence, but also in some situations generate indirect positive effects between prey species.

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                                                                                                                                                                                                                                  • Vasseur, D. A., P. Amarasekare, V. Rudolf, and J. Levine. 2011. Eco-evolutionary dynamics enable coexistence via neighbor-dependent selection. American Naturalist 178:96–109.

                                                                                                                                                                                                                                    DOI: 10.1086/662161Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                                                                                    Presents a mathematical model that combines population dynamics and quantitative genetics to investigate whether selection driven by competition could allow the coexistence of competitors that otherwise exclude each other. It introduces a mechanism of neighbor-dependent selection, which allows coexistence via population cycles driven by intransitive interactions.

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