Density dependence in resource exploitation: empirical test of Levins' metapopulation model

Levins' model of metapopulation dynamics is modified to incorporate variabl e degrees of density dependence in the per capita exploitation of resource patches. We demonstrate a simple means of testing for this density dependen ce in a sample of metapopulations, each at its equilibrium balance of local colonization to extinction. The fraction of habitable unoccupied patches e quilibrates to a constant number under the null model of density independen t colonization, and tu a constant proportion under strong density dependenc e. We compare the null model to two density dependent alternatives, using d ata on exploitation of nest boxes by collared flycatchers Ficedula albicoll is. The analysis show shows predicted trends in the equilibrium unoccupied fraction are similar for both spatial interference and net immigration. Thi s needs to be recognized, since the null hypothesis of a constant unused re source applies also to the dynamics of consumable resources, where it is ex pressed in a constant stock of uneaten prey at the dynamic equilibrium of p redators to prey.