INFLUENCE OF SEASON AND A SYMPATRIC CONGENER ON HABITAT USE BY STEPHENS KANGAROO RAT

We examined habitat used by the endangered Stephens' kangaroo rat (Dip odomys stephensi) in different seasons and assessed whether this may b e influenced by a sympatric congener, the Pacific kangaroo rat (Dipodo mys agilis). Trapping on three plots over 2 years revealed these speci es were rarely captured at the same trap stations. Spatial segregation was highly significant when both species were at high density. The sa ptial distribution of these species was temporally stable where both s pecies were relatively abundant, but where D. agilis was relatively un common the distribution of D. stephensi varied from one census to anot her. The abundance of three microhabitats (grass, debris, and bare gro und) followed a regular seasonal patter of variation that was consiste nt across 2 years of substantially different rainfall. A canonical dis criminant analysis showed that the five quantified microhabitats (thos e above and bush and rock cover) provided highly significant discrimin ation between the trap stations occupied by the two species. Dipodomys stephensi was associated with trap stations where grass cover and bar e ground were abundant but where bush and rock were uncommon. Dipodomy s agilis was associated with stations that had large amounts of bare g round and average abundances of bush and rock cover. The spatial segre gation 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 dispe rsal corridors of open habitat to link areas of suitable habitat where non presently exist. Each of these options may be needed to maintain viable populations in all reserves designated for the conservation of D. stephensi.