Body Temperature and Metabolism in Subspecies of Peromyscus from Arid and Mesic Environments

Abstract

INTRODUCTION The faunas of our southwestern deserts are rich in small birds and mammals. These homeotherms must have established a harmonious balance between their requirements and the problems presented by the extreme conditions in such an environment. A scarcity of water coupled with high environmental temperatures accentuates the difficulty of thermoregulation in exposed animals, since regulation with a small differential in temperature between the body and the environment is dependent upon evaporative cooling. Estivation (Howell, 1938; Bartholomew and Cade, 1957; Lyman and Chatfield, 1955; Bartholomew and MacMillen, 1961), burrowing (Sumner, 1925, Vorhies, 1945; Schmidt-Nielsens, 1951), and nocturnal activity (Sumner, 1925, Vorhies, 1945; Schmidt-Nielsens, 1951; Dawson, 1955) are considered as physiological and behavioral adaptations exhibited by desert homeotherms allowing a resident to evade the most extreme conditions. Another desert adaptation is the production of a concentrated urine, demonstrated in Dipodomys (Schmidt-Nielsens, 1951) and to a lesser extent in Citellus leucufrus (Hudson, 1960), which at its extreme may permit a desert species to live entirely on the water produced by oxidation. Other species like the wood rat, Neoto ma albigula, depend upon succulent vegetation for their water supply (Vorhies, 1945; Schmidt-Nielsen, 1948). But adaptative modifications of the body temperature and metabolism to desert conditions have not been extensively sought for. Temperature in most mammals is maintained relatively independent of moderate changes in environmental temperature. These body temperatures are not