Ecological Character Displacement

Abstract

Some morphological differences between closely related species living in the same environment have been enhanced by natural selection resulting from competition between the species or the negative effects of interbreeding. These evolutionary changes are known as ecological and reproductive character displacement, respectively. Ecological character displacement, the subject of this article, helps us to understand how complex communities are built up from simpler ones through ecological adjustments of the constituent species. It also may be involved in the late stages in speciation when formerly allopatric populations come together in sympatry. Examples are given from studies of birds in nature and sticklebacks in experiments. There are few cases of ecological character displacement in nature where the evidence is sufficiently strong to demonstrate evolution by natural selection and to rule out alternative explanations of the causes. These have been supplemented by experiments: there is scope and need for more. Key Concepts: Character displacement is a process of evolutionary divergence of coexisting species. Competition for resources, such as food, is reduced as a result of divergence. Natural selection causes the evolutionary change. Closely related species differ in morphology more in sympatry than in allopatry. Experiments attempt to recreate conditions that are conducive to character displacement in nature. Solitary species are released from competition and broaden their ecological niches. Character displacement helps to explain how complex communities of potential competitors develop from simple ones. Character displacement is one of several types of evolutionary adjustments made by coexisting species. Its signature should be seen most clearly in young adaptive radiations. The main question about character displacement is not whether it occurs but how important it is. Keywords: divergence; competition; food; natural selection; evolution; adaptive radiation