Three sympatric species of Neotoma: dietary specialization and coexistence.

ABSTRACT

Three sympatric species of Neotoma occur in the southern Great Basin Desert in northern Arizona. Observations and experiments from 1980-1984 focused on diet and den selection to determine to what extent woodrats partition available food and shelter. Analyses included microscopic inspection of feces from live-trapped animals, forage moisture content, and seasonal habitat utilization. Each species of woodrat was found to selectively forage on a different genus of the three evergreens on the study site N. albigula was the only species to eat appreciable amounts of Yucca, while N. devia, specialized on Ephedra epidermis, and N. stephensi on Juniperus. Observations in the laboratory showed a linear dominance hierarchy where the larger species dominated smaller ones, i.e., N. albigula>N. stephensi>N. devia. To determine if such a hierarchy existed in the field, the behaviorally dominant species (N. albigula and N. stephensi) were continually removed (from a 25 ha experimental plot) over a 12-month period leaving only the subordinate species (N. devia) in the area. In these experiments, 40% of the "dominant"-species dens became occupied by 20 of the "subordinate"-species on the removal plot, whereas there were no interspecific den site (n=39) changes among species on the control plot. Removal of the two dominant Neotoma spp resulted in an increase of N. devia from a pre-removal high of 16 to a post-removal population of 26 individuals. These data suggest that while these woodrats may not compete for food, the subordinate species compete with the dominant species for den sites, prime dens being sequestered by the behaviorally dominant species.