Ecological Implications of Resource Depression

Abstract

Resource depression is an important component of predation which may be independent of the actual amount of exploitation of the prey. In featured environments, where behavioral and microhabitat changes in the prey are important, depression due to these factors may be more important than exploitation depression. If so, then the straightforward measurement of overlap of diets of predators may be very misleading. The susceptibility of the prey to depression and the relative importance of exploitation, behavioral and microhabitat depression, should be incorporated into an analysis of the significance of differences in foraging mode and time of foraging on potential competition. Seeds constitute a resource readily depressed by exploitation but without behavioral or microhabitat shifts. For such a resource the time of day of exploitation would presumably be of no competitive significance, but the mode of searching might be. A bird capable of gaping, probing or scratching should find seeds not available to a surface gleaner. Herbivorous insects exhibit strong behavioral and microhabitat shifts, and slight differences in the timing of exploitation and order of appearance of predators might be important in the kinds and number of prey found. For predators on these prey types, divergence in searching mode and microhabitat selection may be more critical in reducing competition than the taxonomic overlap in prey taken. Such considerations need to be programmed into conceptual analyses of predation and competition more than they have heretofore.