Altitudinal Zonation of Chipmunks (Eutamias): Adaptations to Aridity and High Temperature

Abstract

Fecal, urinary and evaporative water losses were mea- sured at 15 C, 50-75% relative humidity for four species of western chipmunks (Eutamias) which are contiguously allopatric and alti- tudinally zoned on the eastern slope of the Sierra Nevada, California. Evaporative loss and hyperthermia were also studied for acute exposures to 25, 35 and 40 C. Differences in total water budgets, calculated for 35 C and 11% relative humidity are not important in determining the lines of contact, starting from the alpine and descending toward the desert, between E. alpinus and E. speciosus or between E. speciosus and E. amoenus. But they may play a role in preventing E. am,oenus from colonizing the desert sagebrush habitat occupied by E. minimus. E. minimus can be active in the open areas of the hot, arid sagebrush desert by minimizing evaporative water loss and tolerating increased body heat content; this species frequently retreats to, its burrows to un- load excess body heat. When large patches of shade are available from pifion pines the aggressively dominant E. amoenus can occupy the sage- brush habitat. Hence, in the field area of this study the line of contact between E. amoenus and E. minimus coincides with the lower limits of the pifion pine.