Life Spans of Dipodomys and Perognathus in the Mojave Desert

Abstract

Rodent populations were studied by live-trapping in four 20-acre plots for a 2½-year period. Three of the plots were fenced to prevent dispersal. One of the fenced areas was irradiated at a low level; the rodents received an average of 1 r/day. The life span of a rodent was defined as the time between the first and last appearance in the trapping records. Mean life spans in the fenced plots that were not irradiated were between 3.7 and 5.0 months for Perognathus formosus, P. longimembris, Dipodomys merriami and D. microps. Mean life spans were shorter in the irradiated plot and shortest in the unfenced plot. The values for the unfenced plot reflect the additional influences of dispersal and kit fox predation. The kit fox is the only important mammalian predator, but accounts for an insignificant amount of mortality in the rodent population. The red racer is a predator of undetermined importance. Greatest mortality occurs in the few months following first capture. Twenty-five P. longimembris survived from 3 to 5 years, a remarkably long time for a small (6 to 8 g) mammal. Periodic torpor probably aids their survival.