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III.19 Evolution of Communities and Ecosystems Nicolas Loeuille OUTLINE 1. How does evolution affect communities and ecosystems? 2. The ecological implications of single-species evolution 3. Pairwise coevolution and ecosystem functioning: Plant–herbivore coevolution 4. Diffuse coevolution and complex adaptive systems 5. Multiple levels of selection and community evolution 6. Impact of species evolution and coevolution on abiotic components of ecosystems Although much of evolutionary biology focuses on explaining phenotypic trait variation and on understanding the genetic basis for this variation, evolution can also affect the structure and functioning of communities and ecosystems. Evolution by natural selection discriminates among individuals based on their relative fitness such that the process of evolution is linked to demographic parameters. Therefore , it is expected that the evolution frequently will affect the demographic dynamics of the evolving species. Effects of evolution may extend further and affect the composition of the entire community as well as energy and nutrient fluxes at the ecosystem scale. Here, I summarize the effects of evolution on community and ecosystem properties along a gradient of increasing evolutionary complexity , from the effects of single-species evolution to the effects of the coevolution of two interacting species, and finally ending with the effects of the coevolution of many species. GLOSSARY coevolution. A strict definition of coevolution has been given by D. H. Janzen (1980): ‘‘Coevolution may be usefully defined as an evolutionary change in a trait of the individuals in one population in response to a trait of the individuals of a second population, followed by an evolutionary response by the second population to the change in the first.’’ As this definition requires reciprocal evolutionary feedbacks between two populations, it directly applies to what is called pairwise coevolution. community genetics. Initially defined by J. Antonovics (1992), a more recent definition of community genetics may be found in T. G. Whitham and colleagues (2003, see Further Reading): ‘‘The role of intraspecific genetic variation in affecting community organization or ecosystem dynamics.’’ complex adaptive systems. Initially defined by J. Holland (1995), the definition of complex adaptive systems has been simplified by S. A. Levin (1998, see Further Reading). A system is a complex adaptive system if it fulfills three characteristics: (1) individuality and diversity of components; (2) localized interactions between those components ; and (3) an autonomous process that selects a subset for replication and enhancement from among components, based on the results of local interactions. diffuse coevolution. The extension of pairwise coevolution to multiple species. Diffuse coevolution implies the coevolution of not just two populations, as in Janzen’s definition, but three or more. Under diffuse coevolution, trait variations in populations A and B have reciprocal effects not only on each other but also on any other number of other populations in the community. niche construction. From K. N. Laland and colleagues (1999, see Further Reading): the modification of local resource distributions by organisms in a way that influences both their ecosystems and the evolution of their resource-dependent traits. 1. HOW DOES EVOLUTION AFFECT COMMUNITIES AND ECOSYSTEMS? Phenotypic Variation as the Main Focus of Evolutionary Studies Historically, evolutionary biologists have focused on understanding why certain phenotypes are observed in a given population. Key questions include the reasons for the dominance of certain phenotypes and the maintenance of polymorphisms (two or more distinct phenotypes ). The classical example of Charles Darwin’s finches perfectly illustrates this approach. Darwin observed the beak characteristics of different species of finches and how such variation might be related to the food consumed by these species. He linked the observed traits and their diversity to selective pressures. Afterward , development of genetics provided a hereditary mechanism for phenotypic transmission within lineages , but the focus of most evolutionary research has remained the same: the causes of phenotypic variation within and among populations. After this important issue, the next step is to evaluate the effects of phenotypic variation on community and ecosystem processes at larger spatial scales. Is There Any Reason to Think That Evolution Will Influence Communities and Ecosystems? With the phrase ‘‘survival of the fittest,’’ Darwin coined the idea that observed traits are maintained because they provide an advantage to the individual in terms of survival or fecundity. This idea requires a definition of the fitness of an individual. J.B.S. Haldane defined individual fitness in the 1920s simply as the total number of offspring an individual begets during her lifetime. Fitness as defined...


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