Resource Depletion and Habitat Segregation by Competitors Under Predation Hazard

Abstract

Individuals of different sizes in size-structured populations often differ greatly in the use of resources and/or space. Spectacular examples include shifts, within a lifetime, from carnivory to herbivory (e.g., some turtles; Clark and Gibbons 1969), or from herbivory to carnivory (e.g., some copepods; Neill and Peacock 1980), or from aquatic to terrestrial habitats (e.g., many amphibians). Many other species show large shifts in prey size or habitat use as they grow, but yet other species show little difference across sizes (Fraser 1976; Polis 1984; Werner and Gilliam 1984; Persson this Vol.). Thus, patterns of resource and habitat use within a species vary from complete segregation between two given size classes, to partial overlap, to complete overlap. The presence or absence of such diet or habitat segregation between different size classes can greatly affect population structure and dynamics. For example, the degree of overlap between different size classes influences population stability, and the intensity of competition between classes influences, in interesting ways, whether increases in the density of a given class increases or decreases the density of other classes (Tschumy 1982; Mittelbach and Chesson 1987; Ebenman this Vol.).