The fitness consequences of variation in resting metabolic rate in juvenile North American red squirrels (Tamiasciurus hudsonicus)

Abstract

Resting metabolic rate (RMR) is the minimum energy expenditure necessary for survival. RMR varies widely both among and within species and a central question in evolutionary physiology concerns the functional basis for this variation. Juvenile North American red squirrels were used to investigate fitness consequences of variation in RMR by considering how expenditure relates to differences in food availability and to overwinter survival. Additionally, this thesis examines whether red squirrels exhibit phenotypic plasticity in RMR in response to varying levels of food availability. Results indicate that heavier juveniles with relatively low RMRs were more likely to survive overwinter. Moreover, these juveniles were capable of allocating more energy towards mechanical work and possessed larger food stores. Food supplemented yearlings exhibited higher RMRs than unsupplemented controls at the onset of the breeding season, while no difference in RMR was detected following termination of supplementation.