Data from: Individual variation in energy-saving heterothermy affects survival and reproductive success

Given fundamental energetic trade-offs among growth, maintenance and
reproduction, individual differences in energy saving should have
consequences for survival and reproductive success. Many endotherms use
periodic heterothermy to reduce energy and water requirements and
individual variation in heterothermy should have fitness consequences.
However, attempts to disentangle individual- and population-level
variation in heterothermy are scarce. Here, we quantified patterns of
heterothermy of 55 free-ranging eastern chipmunks (Tamias striatus),
food-hoarding hibernators. Over five hibernation periods, we obtained a
total of 7108 daily individual heterothermy indices (median: 118 per
individual). Based on an individual reaction norm approach, we found that
the use of heterothermy was repeatable and varied among individuals of the
same population under similar environmental conditions. This
among-individual variation had consequences for winter survival and
reproductive success. Individuals using less heterothermy at the beginning
of the winter had decreased survival in resource-rich but not in
resource-poor years and higher reproductive success in the subsequent
breeding season. These results support the hypothesis that fluctuating
selection maintains heterothermic diversity and suggest that
individualized ecophysiology can contribute to a more thorough
understanding of the evolution of energy-saving strategies in endotherms.