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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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Comparison of predicted average polar bear weight loss to field measurements.Average weight losses (±S.E.) for bears of all sizes and body condition predicted by Niche Mapper simulations compared to weight losses from field studies of bears in the western Hudson Bay population during the ice-free period. The Derocher & Stirling data [67] is for adult males and females. The Polischuk et al. [60] and Atkinson et al. study [59] male data presented include both adult and subadult males, and for Polischuk et al., females with yearlings.
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pone-0072863-g005: Comparison of predicted average polar bear weight loss to field measurements.Average weight losses (±S.E.) for bears of all sizes and body condition predicted by Niche Mapper simulations compared to weight losses from field studies of bears in the western Hudson Bay population during the ice-free period. The Derocher & Stirling data [67] is for adult males and females. The Polischuk et al. [60] and Atkinson et al. study [59] male data presented include both adult and subadult males, and for Polischuk et al., females with yearlings.

Mentions: Simulations in which bears used higher percentages of fat for energetic demands (e.g., Sim1; 94.56%) lost less weight than those using lower percentages of fat (Fig. 5). For males, Sim1 predicted average weight loss lower than the average weight loss in two of the three studies reporting weight loss, and Sim3 (88.56% fat usage) predicted weight losses greater than all three of the reported weight losses (Fig. 5). For females, Sim1 predicted weight losses lower than published studies, while the other two simulations predicted weight losses in between the two published studies.


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

Mathewson PD, Porter WP - PLoS ONE (2013)

Comparison of predicted average polar bear weight loss to field measurements.Average weight losses (±S.E.) for bears of all sizes and body condition predicted by Niche Mapper simulations compared to weight losses from field studies of bears in the western Hudson Bay population during the ice-free period. The Derocher & Stirling data [67] is for adult males and females. The Polischuk et al. [60] and Atkinson et al. study [59] male data presented include both adult and subadult males, and for Polischuk et al., females with yearlings.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0072863-g005: Comparison of predicted average polar bear weight loss to field measurements.Average weight losses (±S.E.) for bears of all sizes and body condition predicted by Niche Mapper simulations compared to weight losses from field studies of bears in the western Hudson Bay population during the ice-free period. The Derocher & Stirling data [67] is for adult males and females. The Polischuk et al. [60] and Atkinson et al. study [59] male data presented include both adult and subadult males, and for Polischuk et al., females with yearlings.
Mentions: Simulations in which bears used higher percentages of fat for energetic demands (e.g., Sim1; 94.56%) lost less weight than those using lower percentages of fat (Fig. 5). For males, Sim1 predicted average weight loss lower than the average weight loss in two of the three studies reporting weight loss, and Sim3 (88.56% fat usage) predicted weight losses greater than all three of the reported weight losses (Fig. 5). For females, Sim1 predicted weight losses lower than published studies, while the other two simulations predicted weight losses in between the two published studies.

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