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Simulating polar bear energetics during a seasonal fast using a mechanistic model.

Mathewson PD, Porter WP - PLoS ONE (2013)

Bottom Line: Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast.A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%.Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.

View Article: PubMed Central - PubMed

Affiliation: Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.

ABSTRACT
In this study we tested the ability of a mechanistic model (Niche Mapper™) to accurately model adult, non-denning polar bear (Ursus maritimus) energetics while fasting during the ice-free season in the western Hudson Bay. The model uses a steady state heat balance approach, which calculates the metabolic rate that will allow an animal to maintain its core temperature in its particular microclimate conditions. Predicted weight loss for a 120 day fast typical of the 1990s was comparable to empirical studies of the population, and the model was able to reach a heat balance at the target metabolic rate for the entire fast, supporting use of the model to explore the impacts of climate change on polar bears. Niche Mapper predicted that all but the poorest condition bears would survive a 120 day fast under current climate conditions. When the fast extended to 180 days, Niche Mapper predicted mortality of up to 18% for males. Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast. A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%. Niche Mapper explicitly links an animal's energetics to environmental conditions and thus can be a valuable tool to help inform predictions of climate-related population changes. Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.

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Polar bear torso circumference calculated by Niche Mapper compared to expected axillary girth.Torso cylinder circumferences modeled by Niche Mapper for bears of average body condition (total mass = 2.25× structural mass) compared to expected axillary girth for polar bears of different body lengths based on predictive equations from field study measurements of wild polar bears [66]. The error bars for the Thiemann et al. (1980–1996 data) represent the average 5.84% difference between predicted and actual measurements reported in the study.
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pone-0072863-g002: Polar bear torso circumference calculated by Niche Mapper compared to expected axillary girth.Torso cylinder circumferences modeled by Niche Mapper for bears of average body condition (total mass = 2.25× structural mass) compared to expected axillary girth for polar bears of different body lengths based on predictive equations from field study measurements of wild polar bears [66]. The error bars for the Thiemann et al. (1980–1996 data) represent the average 5.84% difference between predicted and actual measurements reported in the study.

Mentions: Total body surface areas and torso dimensions modeled on bears in average body conditions compare favorably to empirical measurements across a wide range of body sizes (Figs. 1,2). Calculated fur surface areas differed by <6% (average: 1.4%) and skin surface areas by <7% (average: 5.4%) from areas expected based on allometric equations developed from measurements on live bears [55]. Similarly, radiant fur temperatures calculated by Niche Mapper correspond with those measured by Best [48] across a range of temperatures and wind speeds, differing from measured temperatures by <7.5% (average: 4.5%) (Fig. 3). Niche Mapper’s model denning bear in a curled position in the reported den conditions was predicted to have a steady state metabolic between the average standard metabolic rate and the lowest observed metabolic rate reported by Watts [56] (Fig. 4). When uncurled, the predicted steady state metabolic rate was greater than the average standard metabolic rate.


Simulating polar bear energetics during a seasonal fast using a mechanistic model.

Mathewson PD, Porter WP - PLoS ONE (2013)

Polar bear torso circumference calculated by Niche Mapper compared to expected axillary girth.Torso cylinder circumferences modeled by Niche Mapper for bears of average body condition (total mass = 2.25× structural mass) compared to expected axillary girth for polar bears of different body lengths based on predictive equations from field study measurements of wild polar bears [66]. The error bars for the Thiemann et al. (1980–1996 data) represent the average 5.84% difference between predicted and actual measurements reported in the study.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3760880&req=5

pone-0072863-g002: Polar bear torso circumference calculated by Niche Mapper compared to expected axillary girth.Torso cylinder circumferences modeled by Niche Mapper for bears of average body condition (total mass = 2.25× structural mass) compared to expected axillary girth for polar bears of different body lengths based on predictive equations from field study measurements of wild polar bears [66]. The error bars for the Thiemann et al. (1980–1996 data) represent the average 5.84% difference between predicted and actual measurements reported in the study.
Mentions: Total body surface areas and torso dimensions modeled on bears in average body conditions compare favorably to empirical measurements across a wide range of body sizes (Figs. 1,2). Calculated fur surface areas differed by <6% (average: 1.4%) and skin surface areas by <7% (average: 5.4%) from areas expected based on allometric equations developed from measurements on live bears [55]. Similarly, radiant fur temperatures calculated by Niche Mapper correspond with those measured by Best [48] across a range of temperatures and wind speeds, differing from measured temperatures by <7.5% (average: 4.5%) (Fig. 3). Niche Mapper’s model denning bear in a curled position in the reported den conditions was predicted to have a steady state metabolic between the average standard metabolic rate and the lowest observed metabolic rate reported by Watts [56] (Fig. 4). When uncurled, the predicted steady state metabolic rate was greater than the average standard metabolic rate.

Bottom Line: Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast.A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%.Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.

View Article: PubMed Central - PubMed

Affiliation: Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.

ABSTRACT
In this study we tested the ability of a mechanistic model (Niche Mapper™) to accurately model adult, non-denning polar bear (Ursus maritimus) energetics while fasting during the ice-free season in the western Hudson Bay. The model uses a steady state heat balance approach, which calculates the metabolic rate that will allow an animal to maintain its core temperature in its particular microclimate conditions. Predicted weight loss for a 120 day fast typical of the 1990s was comparable to empirical studies of the population, and the model was able to reach a heat balance at the target metabolic rate for the entire fast, supporting use of the model to explore the impacts of climate change on polar bears. Niche Mapper predicted that all but the poorest condition bears would survive a 120 day fast under current climate conditions. When the fast extended to 180 days, Niche Mapper predicted mortality of up to 18% for males. Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast. A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%. Niche Mapper explicitly links an animal's energetics to environmental conditions and thus can be a valuable tool to help inform predictions of climate-related population changes. Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.

Show MeSH
Related in: MedlinePlus