Mechanisms for Coexistence Among Three Species of Dipodomys: Habitat Selection and an Alternative

High—resolution radio—tracking was used to study the habitat affinities of Dipodomys merriami, D. ordii, and D. spectabilis in an area of mixed shrubs and grasses in central New Mexico. Detailed habitat maps were examined to place the locations of stops in one of seven habitat classes, and preferences were identified by comparing the number and duration of stops with that expected if habitat use were proportional to habitat abundance. Neither Dipodomys merriami nor Dipodomys ordii used habitats in the available proportions. Both stopped more frequently at burrow locations beneath Larrea, the dominant shrub, and also used sand dunes more than expected. Dipodomys merriami avoided grassy areas entirely. These two species also used significantly different mixes of habitats. Analyses limited to stops either in the open or beneath shrubs showed that D. ordii preferred the shrubs and that D. merriami had no relative preference for either habitat. Limited observations of D. spectabilis showed that they avoided shrubby habitats. These results support the hypothesis that habitat selection facilitates coexistence between Ord's and Merriam's Kangaroo rats. However, the adequacy of this mechanism to account fully for the coexistence of these species is questioned. An alternative, nonequilibrium hypothesis is proposed, which is based on the assumptions that neither species has a clear competitive advantage in the mixture of habitats where they coexist, and that the course of the interaction is frequently disturbed by migration from nearby, allopatric populations.