A body composition model to estimate mammalian energy stores and metabolic rates from body mass and body length, with application to polar bears

Abstract

SUMMARYMany species experience large fluctuations in food availability and depend on energy from fat and protein stores for survival, reproduction and growth. Body condition and, more specifically, energy stores thus constitute key variables in the life history of many species. Several indices exist to quantify body condition but none can provide the amount of stored energy. To estimate energy stores in mammals, we propose a body composition model that differentiates between structure and storage of an animal. We develop and parameterize the model specifically for polar bears (Ursus maritimus Phipps) but all concepts are general and the model could be easily adapted to other mammals. The model provides predictive equations to estimate structural mass, storage mass and storage energy from an appropriately chosen measure of body length and total body mass. The model also provides a means to estimate basal metabolic rates from body length and consecutive measurements of total body mass. Model estimates of body composition, structural mass, storage mass and energy density of 970 polar bears from Hudson Bay were consistent with the life history and physiology of polar bears. Metabolic rate estimates of fasting adult males derived from the body composition model corresponded closely to theoretically expected and experimentally measured metabolic rates. Our method is simple, noninvasive and provides considerably more information on the energetic status of individuals than currently available methods.

Corrigendum to “Predicting survival, reproduction and abundance of polar bears under climate change” [Biol. Conserv. 143 (2010) 1612–1622]

“…For this, we used mass and length data from 97 adult males caught in Western Hudson Bay during the on-shore fasting period, and scaled their body masses to an on-shore arrival date of August 1 by using the mass loss curve of Molnár et al (2009) to estimate the population distribution of energy densities at the beginning of the fasting season. We then applied the DEB model shown in Eqs.…”

“…Unfortunately, when scaling the observed body masses to August 1, we incorrectly programmed the mass loss curve of Molnár et al (2009): Instead of the correct equation…”

A circumpolar monitoring framework for polar bears

“…Earlier break-up has been correlated with reduced body condition that is linked to reproductive performance , Molná r et al 2011. This pattern has been well documented in the Western Hudson Bay subpopulation , Stirling and Parkinson 2006) and similar patterns are emerging in more northern subpopulations .…”

“…Changing pregnancy rates could be related to environmental conditions or a host of other factors (e.g., pollution). Assessment of mating success is necessary to interpret pregnancy rates because a depletion of adult males in a population could also lower mating success (see Molná r et al 2008).…”

“…Most studies using M-R also incorporate harvest recovery of marked animals (e.g., Taylor et al , 2009Peacock et al 2012). Both methods have been applied to monitoring survival and have provided estimates (Amstrup and Durner 1995;Derocher and Stirling 1996;Regehr et al 2007Regehr et al , 2010.…”