Temporal Variation, Habitat Selection and Community Structure

Abstract

Isodar theory, a model of density-dependent habitat selection, is used to examine how temporal variation affects community organization. An isodar is a plot of the density of a species in one habitat versus its corresponding density in a second habitat such that an individual's expected fitness in the two habitats is the same. Isodars can also be plotted by using the density in one habitat at different times. Ecological succession modifies habitat, the expected reproductive success of individuals living in the habitat, and thus, population density. These effects can be detected in the slopes and intercepts of isodars. It is possible, therefore, to use density estimates alone to predict the time-course of community structure with ecological succession. The proper protocol for this analysis requires replicated population estimates for each temporal stage as well as simultaneous estimates from adjacent undisturbed controls. Previous empirical studies on mice demonstrate the ability of such analyses to reveal the joint effects of temporal and spatial variation on community structure. Extension of the theory to evaluate the relative use of different habitats shows that niche width can increase, decrease, or remain constant with changes in population density. Niche metrics based on habitat are thus likely to give biased interpretations about density-dependent competitive interaction