Coevolution

Coevolution results from reciprocal evolutionary adaptations of two interacting species. A change in one species acts as a selective force on another species, whose adaptation in turn acts as a selective force on the first species. This linkage of adaptations requires that genetic change in one of the interacting populations of the two species be tied to genetic change in the other population. An example of such dual adaptation that probably qualifies as convolution is the gene-for-gene regulation between a plant species and a species of a virulent pathogen (see Figure 1). In contrast, the aposematic coloration of various tree frogs and the corresponding aversion reactions of various predators do not qualify as coevolution because these are adaptations to multiple species in the community rather than coupled genetic changes in just two interacting species. In fact, the term coevolution may often be used too loosely in describing the adaptations of certain organisms to the presence of other organisms in a community. There is little evidence for true coevolution in most cases of interspecific interactions. Nevertheless, the more generalized adaptation of organisms to other organisms in their environment is a fundamental characteristic of life. At present, much evidence seems to indicate that competition and predation are the key processes driving community dynamics. But this conclusion is based mainly on research in temperate communities. Far fewer data exist for interspecific interactions in tropical communities. In addition, the hypothesis that competition and predation control community structure is being challenged by ecologists exploring the influences of parasitism, disease, mutualism, and commensalism on communities.

Figure 1: Defense response against an avirulent pathogen.

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