Long‐Term Experimental Study of a Chihuahuan Desert Rodent Community: 13 Years of Competition

Abstract

An experimental study of competition between kangaroo rats (Dipodomys spp.) and other sympatric desert rodents using exclosures with "semipermeable" fences has been continuously maintained at a site in the northern Chihuahuan Desert since 1977. A new set of experimental manipulations begun in 1988 at the same site repeated this study. As reported previously for this community, exclusion of three species of Dipodomys from both original and new experimental plots resulted in greater abundances of five species of small granivorous rodents (Chaetodipus penicillatus, Perognathus flavus, Peromyscus eremicus, P. maniculatus, Reithrodontomys megalotis) on these plots relative to controls. In contrast, there were no significant treatment effects on the abundances of insectivorous grasshopper mice (Onychomys spp.). The long time lag before the response by small granivores to Dipodomys removal observed in the original experiment was not repeated in the experiment begun in 1988. Long—term (10 yr) exclusion of kangaroo rats from experimental plots has resulted in changes in vegetative cover, particularly increased grassiness, on these plots relative to controls. We used the repetition of the Dipodomys exclusion experiment in 1988 to evaluate the importance of this potential indirect effect of kangaroo rats on other rodents in this community. By examining differences in rodent capture numbers on the original and new sets of Dipodomys exclusion plots, we could identify four species (C. penicillatus, Perognathus flavus, Peromyscus eremicus, P. maniculatus) whose responses to Kangaroo rat removal reflected direct competition from kangaroo rats, one species (R. megalotis) whose response reflected both direct and indirect (via vegetation changes and habitat selection) effects, and two species (Sigmodon hispidus, S. fulviventer) whose responses reflected only vegetation—mediated effects. The continuous presence of competition between small granivores and kangaroo rats over the 13—yr study despite large, specie—specific fluctuations in abundances suggests that competition is pervasive within this community.