Extinction Thresholds in Demographic Models of Territorial Populations

Abstract

A basic demographic model is constructed for territorial species in a region where patches of habitat suitable for survival and reproduction are randomly (or evenly) interspersed with patches of unsuitable habitat. The model predicts the equilibrium occupancy of suitable habitat as a function of the proportion of the region composed of suitable habitat, h, and of the demographic potential of the population, k, which is determined by parameters of the life history and dispersal behavior of individuals. If 0 < k < 1, the demographic potential gives the equilibrium occupancy in a completely suitable region, and the population will become extinct in the region if h $\leq$ 1 - k. Difficulty in finding a mate, the finite extent of the region containing suitable habitat, and serially uncorrelated fluctuations in life history parameters all increase the minimum value of h necessary to sustain a population. Models of this type should be useful for predicting the effects of habitat destruction and fragmentation, or habitat improvement, on the population sizes of rare or endangered species with territorial behavior.