Environments of Kangaroo Rats (Dipodomys) and Effects of Environmental Change on Populations in Southern Nevada

Abstract

Climates and plant components of environments of the heteromyid rodents Dipodomys merriami, D. microps, and D. deserti are characterized and compared on sites over 2600 square kilometers in central-southern Nevada. Sites compared are those with the 20 highest-density populations each of D. merriami and D. microps, and all sites with D. deserti, from among 58 undisturbed communities where rodent numbers were established by five consecutive years of censusing. The study areas were in eight drainage basins of the Nevada Test Site, at elevations of 915 to 1850 meters (m), and included Mojave, Great Basin, and transition desert systems. Other parameters measured on each site, and compared for the site groups, are rainfall, maximum and minimum air temperatures, and various parameters for all plant components of the systems. Plant data were collected seasonally with the rodent data, whereas the climatic data were for 10 years. Distributions of D. merriami and D. deserti were correlated with the low shrub cover and low mean precipitation/mean temperature (P/T) ratios of the Mojave Desert Larrea communities. Distributions and higher densities of D. microps were closely correlated with the high shrub cover and high P /T ratios of the Coleogyne and Grayia-Lycium communities of the transition, and Artemisia of the Great Basin Desert. On the compared sites either D. merriami or D. microps usually occurred to the near exclusion of the other, and none of the plant parameters other than percentage shrub cover distinguished the two rodent environments. Restriction of D. microps to environments with high mean rainfall supports recent physiological evidence by others that this species may have the highest bodywater turnover rate and lowest urine-concentrating ability in the genus. On nine other sites shrub cover had been destroyed (and surface soils modified) by nuclear detonations, fire, or blading prior to the measurements period. Three of the sites were in declining ionizing-radiation fields. Regardless of nature of origin of the disturbance, there was a rapid and usually nearly complete replacement of D. microps by large D. merriami populations following the disturbance. The only change in plant parameters consistent among the sites was the large reduction in shrub cover. Occupancy of these sites by D. merriami was in accord with its ability to live with low shrub cover. Disappearance of D. microps was evidently related to its corresponding requirement of high shrub cover, suggesting a vulnerability to elimination by predators where there are few or no shrubs in the environment.