Population Ecology of a Desert Rodent: Dipodomys Merriami in the Chihuahuan Desert

Abstract

We show that the extremely flexible life history and other facultative behaviors of the kangaroo rat, Dipodomys merriami, facilitate adult survival and enable this small mammal to maintain remarkably stable populations despite wide, unpredictable fluctuations in its desert environment. Mark—recapture methods provided data on population density, growth, reproduction, dispersal, and survival for a population of D. merriami in the Chihuahuan Desert of southeastern Arizona from 1978 through 1984. Population density showed both annual and interannual fluctuations, but varied only from °3 to 15 individuals/ha. The life history is characterized by long survival (up to at least 3.5 yr), modest and variable reproductive effort (zero to at least two litters per year, and an average of two young per litter), slow growth and maturation of young (at least 3 mo from birth to reproductive maturity), and frequent, facultative dispersal of adults as well as juveniles (75% of the males and 59% of the females that lived >4 mo dispersed). This combination of life history traits enabled D. merriami to confine reproduction to favorable periods, with the result that although adults of both sexes showed a loss of body mass associated with reproduction, there was no evidence that they experienced increased risk of mortality. Frequent and male—biased dispersal of adults is probably not unique to this species. Most standard methods of analyzing mark—recapture data probably underestimate the frequency of dispersal and its effects on sex ratio and genetic structure.