Dependence of Desert Rodents on Winter Annuals and Precipitation

Winter annual parameters, postreproduction rodent densities, and precipitation, were recorded over 5 consecutive years on 15 sites in Jackass Flats, southern Nevada. When the rain critical to autumn germination came, winter annuals were present during autumn—to—spring, and there was spring reproduction in the rodents (as indicated by summer densities). When the critical rain failed to come, winter annuals populations were negligible and the rodents did not reproduce in the spring. One season, half of the study sites received autumn rainfall adequate for germination, and the other half did not; summer rodent densities increased on the former and markedly decreased on the latter. Following extraordinary heavy early spring rains, following an autumn essentially without rain, there was partially successful germination in early spring, and rodent reproduction occurred in the summer. It is concluded that occurrence and failure of reproduction in desert rodents are correlated with the presence and absence of winter annuals in the environment. The data suggest that dietary water (and vitamins), available in winter annual vegetation prior to or at time of onset of the breeding season, are requirements in the physiology of reproduction of heteromyid species.