Climatic adaptation in the energetics of heteromyid rodents

Abstract

1. 1. The temperature regulation and heat production of two heteromyid rodents, Heteromys anomalus and Dipodomys deserti, were studied. 2. 2. Heteromys has a high basal rate and a high minimal thermal conductance: D. deserti has a low basal rate and a low conductance. Other heteromyids, all of which, like D. deserti, live in arid environments, also have low basal rates and low thermal conductances. The depression of metabolism and conductance is most pronounced in small pocket-mice ( Perognathus). 3. 3. Low basal rates are an alternative to the production of a concentrated urine as a means of reducing water turnover in mammals with low water intake. Thus. among kangaroo-rats, species that live in mesic microenvironments and feed upon foods of a high water content, such as D. microps, have higher relative basal rates than other species. Heteromys differs from other heteromyids by inhabiting tropical rainforests, where water conservation is of minimal importance. Low basal rates may also be an adaptation to seasonally variable mast crops. 4. 4. In the maintenance of a temperature differential with the environment, low conductances compensate for low rates of metabolism, especially at small body sizes. 5. 5. These data are interpreted to mean that phylogeny, independent of ecological relations, has little influence on the energetics of endotherms.