In this paper I review the contributions of analytic and experimental research on intraguild predation and interspecific competition to our understanding of population regulation in plethodontid salamanders. Henry Wilbur's model of population regulation in amphibians serves as a framework for the arguments. Much of the discussion is based on studies of eastern North American plethodontids that have been the focus of most of the research. Ensembles of plethodontids in this region include species with complex life cycles (i.e., larval development) and simple life cycles (i.e., direct development). Interactions between members of these two life-history categories appear to be weaker than those within categories. Whereas there is no definitive evidence of factors that regulate populations of plethodontid salamanders, interspecific competition and intraguild predation do appear to contribute in some ensembles. Food and space have been identified as limiting resources in interspecific competition. Although predation of larger on smaller salamanders may be relatively rare in nature, the threat of predation appears to promote behavioral responses in members of the smaller species that reduce risks but may lower fitness through other effects. The role of extralimital predators and competitors in regulation of these salamanders is largely untested. Ideally, future research should involve manipulative experiments on unenclosed field plots that examine effects of resources, intraguild competitors and predators, and extralimital predators on populations of key species of plethodontids.

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