Seasonal Reproductive Patterns in Five Coexisting California Desert Rodent Species

For 3 yr we studied the reproductive responses of desert rodents in the Owens Valley of eastern California (average annual precipitation 14 cm): four nocturnal heteromyids–the kangaroo rats Dipodomys microps and D. merriami and the pocket mice Perognathus formosus and P. longimembris–and one diurnal sciurid, the antelope ground squirrel, Ammospermophilus leucurus. Reproductive status was assessed by autopsies of adults trapped at approximately monthly intervals. Reproduction differed conspicuously among the five species. Our analysis illustrates effects of body size, phylogenetic association, and adaptation to the desert environment upon reproductive performances and associated life—history parameters. Most breeding occurs in late winter and early spring. Winter rains cause a series of pulses in vegetation growth and an attendant increase in availability of water in food plants, which contribute to rodent reproduction. Among the four heteromyids, onset of breeding is sequential according to body size, wit...