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

H. Craig Heller and Thomas Poulson
The American Midland Naturalist
Vol. 87, No. 2 (Apr., 1972), pp. 296-313
DOI: 10.2307/2423563
Stable URL: http://www.jstor.org/stable/2423563
Page Count: 18
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Altitudinal Zonation of Chipmunks (Eutamias): Adaptations to Aridity and High Temperature
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Abstract

Fecal, urinary and evaporative water losses were measured at 15 C, 50-75% relative humidity for four species of western chipmunks (Eutamias) which are contiguously allopatric and altitudinally 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. amoenus 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 unload excess body heat. When large patches of shade are available from pinon 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 pinon pine.

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