Alternative refuge strategies and their relation to thermophysiology in two sympatric rodents, Parotomys brantsii and Otomys unisulcatus

Abstract

Temperatures were recorded in burrows of Brants' whistling rat, Parotomys brantsii, and lodges of the surface-nesting Karoo bush rat, Otomys unisulcatus, in an attempt to relate within-refuge microclimate to known differences in the species' thermophysiology. The two species were studied simultaneously at the same field site and, hence, under identical climatic conditions. The refuge microclimate of P. brantsii burrows was well buffered from ambient temperature variation, with a narrow average diel temperature range compared with the surface temperature. Maximum burrow temperature was independent of maximum ambient shade temperature. By comparison, the lodges of O. unisulcatus acted as poor buffers from ambient temperature fluctuations, exhibiting greater temperature range. Daily maximum temperature within the lodge was closely correlated with maximum ambient shade temperature. We argue that between-species differences in the thermophysiology of these and other otomyine rodents reflect differences in the thermal properties of their refuges, rather than differences in the degree to which the species in question are adapted to surface conditions in arid or mesic environments.