Prey Species Replacement along a Gradient of Nutrient Enrichment: A Graphical Approach

In this paper I develop a graphical method for visualizing and analyzing the effects of nutrient enrichment on the equilibrium characteristics of 1—predator, many—prey systems. The system considered consists of 1 nonswitching, prey—limited predator feeding on an array of prey species which complete for a single resource. The replacement of 1 prey species by another as eutrophication proceeds is an integral part of this model. The model predicts that prey species which can survive at low nutrient densities should be replaced at higher nutrient densities by species with high maximum rates of increase and by species more resistant to predation. This prediction may be reversed when the predator's population size is controlled by mechanisms which inhibit the predator's ability to respond numerically to increased prey density. Both predictions can be understood in terms of shifts in the relative importances of competition and predation as the nutrient status of a system changes. The graphical method presented should be particularly adaptable to empirical studies of species change along gradients of nutrient enrichment.