Resources: A Graphical-Mechanistic Approach to Competition and Predation

Abstract

The growth response of a population to the resources in a particular environment is used to classify pairs of resources as being either (1) essential, (2) hemi-essential, (3) complementary, (4) perfectly substitutable, (5) antagonistic, or (6) switching. Although nutrition is one important factor determining resource type, the growth response of a population to resources also depends on the interaction between a species' foraging methods and the spatial distribution of the resources. For example, two resources which are nutritionally perfectly substitutable may be operationally switching, antagonistic, or complementary because of spatial heterogeneity. A graphical, equilibrium theory of resource competition allows prediction of the outcome of interactions between several consumers for the various classes of resources. The technique requires information on (1) resource type (growth isoclines), (2) resource preference, (3) resource supply processes, and (4) mortality rates for all species. For all resource types, the major criterion for stable coexistence is that each species consume relatively more of the one resource which more limits its own growth rate.