MICROCLIMATE TEMPERATURE AND ITS ADAPTIVE SIGNIFICANCE IN SIX GEOGRAPHIC RACES OF PEROMYSCUS

Abstract

The ambient temperatures prevailing in the microhabitats of six geographic races of Peromyscus (deer mice) were measured in the summer and winter seasons. A satisfactory method whereby thermistors were hauled by the mice into their microhabitats is described.The results show that the microhabitat provides an environment of moderate, stable temperature where the seasonal extremes of heat and cold can be avoided. Winter microclimate temperatures were never below freezing and were very similar among the habitats despite considerable differences in the gross climates. These observations suggest that there is no significant differential selective pressure for temperature adaptation among the six races, and support the previously reported findings that basal metabolic rate is nonadaptive to climate in Peromyscus.In the distribution and speciation of Peromyscus, the selection and modification of a suitable microclimate are of major temperature-adaptive significance. This particular behavioral method of temperature regulation is potentiated by small body size and is discussed in relation to climatic adaptation of small mammals in general.