The Role of Predation in Shaping and Maintaining the Structure of Communities

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Abstract
Although ecological theorists have shown that frequency-dependent prey selection may permit the coexistence of quite similar competitors, there are compelling reasons to suggest an alternative explanation for the relationship between predation and prey species diversity. Predators which respond to the distribution of prey abundance may maintain prey populations below resource limitation, where optimal utilization patterns are discriminate. More species with discriminate source utilization patterns can coexist than can species with indiscriminate ones. Two observations, one local and ecological and the other global and evolutionary, are explicable in terms of this simple hypothesis concerning the role of predation in shaping and maintaining the structure of communities. Colonizing consumers shape the structure of communities by selecting producers which are using or otherwise would use at least one of their resources indiscriminately. Among the attributes of producers affecting their selection by consumers are those which determine or reflect producer competitive success, population growth rate and frequency, respectively. Thus, predation and competition are balanced at steady-state. In variable environments episodes of recolonization and succession follow severe perturbations, between which milder perturbations are weathered successfully. Although the more diverse communities characterizing low latitudes seem well adapted to naturally occurring environmental variation, they are fragile compared with the less diverse communities of higher latitudes. This is not to say that there is no relationship between species diversity and community stability, but rather that comparing the effects of similar perturbations on temperate and tropical ecosystems is simply inappropriate. The hypothesis about the role of predation in shaping and maintaining the structure of communities suggests that there is such a relationship. That is, a consumer behavioral pattern which seems adaptive is implicated in both, although no causal relationship between species diversity per se and community stability is suggested.