Expenditure freeze the metabolic response of small mammals to….pdfVIP

Ecology Letters, (2005) 8: 1326–1333 doi: 10.1111/j.1461-0248.2005.00839.x L E T T E R Expenditure freeze: the metabolic response of small mammals to cold environments Abstract 1 Murray M. Humphries, * Stan There is renewed focus on the ecological determinants of animal metabolism and recent Boutin,2 Donald W. Thomas,3 comparative analyses support the physiological expectation that the field metabolic rate John D. Ryan,4 Colin Selman,5 (FMR) of homeotherms should increase with declining ambient temperature. However, Andrew G. McAdam,6 Dominique sustained elevation of FMR during prolonged, seasonal cold could be prevented by Berteaux7 and John R. Speakman8 intrinsic limits constraining FMR to some multiple of basal metabolic rate (BMR) or extrinsic limits on resource abundance. We analysed previous measures of mammalian FMR and BMR to establish the effect of ambient temperature on both traits and found no support for intrinsic limitation. We also measured the FMR of a northern population of red squirrels (Tamiasciurus hudsonicus) exposed to ambient temperatures much colder than all but one previous study of mammal FMR. These measurements revealed levels of energy expenditure that are, unexpectedly, among the lowest ever recorded in homeotherms and that actually decrease as it gets colder. Collectively, these resul