Meeting Abstract
Many species use stored energy to hibernate through periods of resource limitation. Hibernation, a physiological state characterized by depressed metabolism and body temperature, is critical to winter survival and reproduction, and therefore has been extensively quantified and modeled. Hibernation consists of alternating phases of extended periods of torpor (low body temperature, low metabolic rate) and energetically costly periodic arousals to normal body temperature. Arousals consist of warming, euthermia, and cooling phases. Warming and euthermic costs are regularly included in energetic models, but although cooling to torpid body temperatures is an important phase of the torpor-arousal cycle, it is often overlooked. When included, cooling cost is assumed to be 67% of warming cost, as measured in a single ground squirrel species, regardless of body size or ambient environment. We derived a model of cooling cost from first principles and validated the model with empirical energetic measurements. We compared the assumed 67% proportional cooling cost with our model-predicted cooling cost for 53 hibernating mammals, including 17 bat species. Our results indicate that using 67% of warming cost only adequately represents cooling cost in ground squirrels. In smaller species, this proportion overestimates cooling cost. Our model allows for the generalization of energetic costs for multiple species using species-specific physiological and morphometric parameters. Our model also allows for predictions over variable environmental conditions, which is imperative in understanding the bioenergetic effects of white-nose syndrome.
