Food limited to habitat limited: Predator prey uncoupled

Although ecologists have been studying the role of predator prey interactions for years, the importance of predation for structuring prey communities is still widely debated. One reason for these equivocal results may be the confounding of predators in food limited systems with those limited by some other factor such as habitat.; Abiotic factors are likely to have differential effects on predator and prey populations thereby intensifying or reducing the role of predator-prey interactions in determining community composition. Taking advantage of changes in abiotic factors due to logging, this study combines several years of observational data with experimental tests to evaluate the impact of a top predator on prey diversity across two habitat types (old growth and 40 year regrowth forest) with potentially differing abiotic limitations. Finally a simulation is used to examine methods of detecting density dependent population regulation.; Results of the field data suggest that the predators and prey studied are differentially affected by habitat differences between the old growth and sites logged forty years prior. Prey abundance at the logged sites is much higher relative to the density of predatory salamander larvae. Predatory larvae in the relatively prey enriched habitat become significantly more selective predators, specializing primarily on one prey type. This specialization effectively uncouples the strong predator prey interactions that structure the benthic community at old growth sites. The resulting assemblage has as much to do with these changes in trophic interactions as it does with biophysical differences.; Consequently, although the constituent members are the same, the mechanisms structuring a community are likely to differ across abiotic gradients, reflecting an integration of the changes due to differences in abiotic variables such as altered resource (e.g. habitat, light) availability and also changes due to differential effects of the alteration of abiotic factors on predator and prey, further altering interactions (e.g. predation) among members of the community. By considering the resource limits over which mechanisms are likely to act, rather than simply constituent members or habitat proximity, we can begin to generalize from one community to another and generate predictive models of community response to change.