Inf luence of Season and a Sympatric Congener on Habitat Use by Stephens’ Kangaroo Rat

We examined habitat use by the endangered Stephens’ kangaroo rat ( Dipodomys stephensi) in different seasons and assessed whether this may be influenced by a sympatric congener, the Pacific kangaroo rat (Dipodomys agilis). Trapping on three plots over 2 years revealed these species were rarely captured at the same trap stations. Spatial segregation was highly significant when both species were at high density. The spatial distribution of these species was temporally stable where both species were relatively abundant, but where D. agilis was relatively uncommon the distribution of D. stephensi varied from one census to another. The abundance of three microhabitats (grass, debris, and bare ground) followed a regular seasonal pattern of variation that was consistent across 2 years of substantially different rainfall. A canonical discriminant analysis showed that the five quantified microhabitats (those above and bush and rock cover) provided highly significant discrimination between the trap stations occupied by the two species. Dipodomys stephensi was associated with trap stations where grass cover and bare ground were abundant but where bush and rock were uncommon. Dipodomys agilis was associated with stations that had large amounts of bare ground and average abundances of bush and rock cover. The spatial segregation of these species appears to be mediated by habitat preferences; D. stephensi prefers grassland and D. agilis prefers sage scrub. This suggests that habitat management for D. stephensi should include (1) controlling the spread of shrubs into grassland and (2) creating dispersal corridors of open habitat to link areas of suitable habitat where none presently exist. Each of these options may be needed to maintain viable populations in all reserves designated for the conservation of D. stephensi.