COEXISTENCE OF A LARGE AND SMALL SPECIES OF DIPODOMYS: EXPLOITATIVE VS. INTERFERENCE COMPETITION.

Abstract

Laboratory experiments have suggested that the coexistence of certain heteromyid rodent species is facilitated through differential use of seed dispersions (clump sizes). Field experiments with the Bannertail kangaroo rat, Dipodomys spectabilis, and Merriam's kangaroo rat, D. merriami, indicate their use of different clump sizes is not sufficiently specialized to permit coexistence. Field experiments based on the assumption that these species interact primarily through aggression demonstrated that during at least one season of the year D. spectabilis excludes the smaller D. merriami from its foraging range. Preliminary characterization of spatial heterogeneity of resource productivity implies that the competitive coexistence of these species is regional and is dependent upon the existence of areas with low productivity that are not economically usable by D. spectabilis. These areas of low productivity may serve as a competitive refuge for D. merriami, facilitating its persistence. A brief review of the evidence for the occurrence of competition between heteromyid species is presented, as is a selected review of the evidence supporting the various hypotheses explaining the competitive coexistence of heteromyid rodents.