On assessing the significance of interspecific competition to guild structure.

A three-phase procedure that can be used to specify the influence of interspecific competition on guild structure is presented. These phases are: 1) measurement of overlap of resource usage (approx= descriptive data); 2) establishment of interaction, which entails the experimental demonstration that the presence of other species leads to altered patterns of resource usage; and 3) demonstration of depressive competition, in which the interaction is shown to be responsible for altered characteristics of populations (eg. population density, age-structure, etc.) or individuals within the populations (eg. fecundity, mortality, relative fitness).