A quantitative model of density-dependent habitat selection: integrating isodar and isoleg theories

Abstract

Numerous conceptual models have been advanced to explain density-dependent habitat selection, but few models address multiple species interactions and even fewer simulate these phenomena. Moreover, the development of quantitative models that incorporate multiple species interactions is in its infancy with existing models being mostly conceptual and limited in application. Herein, I develop a quantitative, simulation model of habitat selection that includes interspecific interactions. The basic model expresses habitat quality in terms of fitness, represented by per capita growth rates, calculated according to the Lotka-Volterra competition equations. Because fitness is assessed via growth rates, this model provides a more accurate representation of distribution patterns than do current models. The development of this model serves two purposes: (1) to permit the quantification of changes in habitat use as a result of intraspecific and interspecific competition, and (2) to unify aspects of habitat selection theory into a general model. In so doing, this model serves as a heuristic device for visualizing isoleg theory, a central theorem of density-dependent habitat selection incorporating interspecific competition (Rosenzweig 1981). Additionally, this model synthesizes two contemporary theories describing habitat selection among competitors; isodar theory (intraspecific competition; Morris 1988) and isoleg theory. Thus, the model explores the combined effects of intra- and interspecific competition, species-specific ecological preferences, and population regulation on species coexistence.