Abstract
Disagreements over the importance of predation in affecting freshwater community structure seem partially attributable to differences in use of essential terms and to a failure to distinguish between the roles of predators in causing and maintaining structure. From analysis of 18 predator-prey, community experiments, I have drawn the following conclusions. Most field experiments show, at best, that predators may depress community density but none demonstrate that these reductions are non-transitory (e.g., evident in the following year). Furthermore, relatively few studies report effects of freshwater predators on species richness or evenness. There is no compelling evidence that predators are the dominant factor in maintaining community structure (i.e., density-dependent regulation of diversity through reduced competitive exclusion). However, it does appear that they contribute to community regulation and may sometimes be an important factor. In contrast, it seems certain that some predators have a role in the causation of diversity through coevolution, size-selective predation, and restrictions on species distributions and community composition. Often these effects are only evident when predators are introduced into systems where they have not coevolved or at least co-occurred with prey for many prey generations.
Published Version
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