Limits...
Predicting climate change impacts on polar bear litter size.

Molnár PK, Derocher AE, Klanjscek T, Lewis MA - Nat Commun (2011)

Bottom Line: In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40-73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55-100% if break-up occurs 2 months earlier.Simultaneously, mean litter size would decrease by 22-67% and 44-100%, respectively.Similar litter size declines may occur in over one-third of the global polar bear population.

View Article: PubMed Central - PubMed

Affiliation: Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2G1. pmolnar@ualberta.ca

ABSTRACT
Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40-73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55-100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22-67% and 44-100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population.

Show MeSH

Related in: MedlinePlus

Predicted changes in litter size as a function of on-shore arrival date.(a, b) Expected proportions of pregnant female polar bears in western Hudson Bay to produce zero (p0, dot-dashed line), one (p1, dashed line), two (p2, solid line) and three (p3, dotted line) cubs as a function of on-shore arrival date under the Early and Late Feeding scenarios, respectively. (c, d) Expected mean litter size (X, dashed line) and expected mean litter size conditional on producing at least one cub (X*, solid line) as a function of on-shore arrival date under Early and Late Feeding, respectively. Dotted lines show 95% confidence intervals. The vertical dotted lines in b and d mark 7 June, the on-shore arrival date before which reproduction becomes impossible with Late Feeding.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3105343&req=5

f3: Predicted changes in litter size as a function of on-shore arrival date.(a, b) Expected proportions of pregnant female polar bears in western Hudson Bay to produce zero (p0, dot-dashed line), one (p1, dashed line), two (p2, solid line) and three (p3, dotted line) cubs as a function of on-shore arrival date under the Early and Late Feeding scenarios, respectively. (c, d) Expected mean litter size (X, dashed line) and expected mean litter size conditional on producing at least one cub (X*, solid line) as a function of on-shore arrival date under Early and Late Feeding, respectively. Dotted lines show 95% confidence intervals. The vertical dotted lines in b and d mark 7 June, the on-shore arrival date before which reproduction becomes impossible with Late Feeding.

Mentions: With earlier on-shore arrival, substantial declines in mean litter size (X) are predicted for both feeding scenarios (Fig. 3). With Early Feeding, we predict X=1.05 if bears come ashore on 1 July and X=0.75 for on-shore arrival on 1 June. Predicted declines are stronger with Late Feeding, with X=0.45 for on-shore arrival on 1 July and no reproduction (X=0) for on-shore arrival before 7 June. For both scenarios, we predict the proportions of females with twins and triplets to decline monotonically and the proportion of non-reproducing females to increase monotonically (Fig. 3a,b). Declines in twin and triplet production will precede declines in the proportion of females having singletons, because some females will move from having twins to having singletons, whereas others will move from having singletons to not reproducing. These predicted changes are consistent with patterns already observed in western Hudson Bay where females are now forced ashore 1–2 weeks earlier than during the early 1990s, and both body condition and reproduction have declined711. More precise data suitable for model validation do not exist, and it is noteworthy in this regard that the predicted litter size changes will be difficult to document if monitoring focuses on X* rather than on X (Fig. 3c,d).


Predicting climate change impacts on polar bear litter size.

Molnár PK, Derocher AE, Klanjscek T, Lewis MA - Nat Commun (2011)

Predicted changes in litter size as a function of on-shore arrival date.(a, b) Expected proportions of pregnant female polar bears in western Hudson Bay to produce zero (p0, dot-dashed line), one (p1, dashed line), two (p2, solid line) and three (p3, dotted line) cubs as a function of on-shore arrival date under the Early and Late Feeding scenarios, respectively. (c, d) Expected mean litter size (X, dashed line) and expected mean litter size conditional on producing at least one cub (X*, solid line) as a function of on-shore arrival date under Early and Late Feeding, respectively. Dotted lines show 95% confidence intervals. The vertical dotted lines in b and d mark 7 June, the on-shore arrival date before which reproduction becomes impossible with Late Feeding.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105343&req=5

f3: Predicted changes in litter size as a function of on-shore arrival date.(a, b) Expected proportions of pregnant female polar bears in western Hudson Bay to produce zero (p0, dot-dashed line), one (p1, dashed line), two (p2, solid line) and three (p3, dotted line) cubs as a function of on-shore arrival date under the Early and Late Feeding scenarios, respectively. (c, d) Expected mean litter size (X, dashed line) and expected mean litter size conditional on producing at least one cub (X*, solid line) as a function of on-shore arrival date under Early and Late Feeding, respectively. Dotted lines show 95% confidence intervals. The vertical dotted lines in b and d mark 7 June, the on-shore arrival date before which reproduction becomes impossible with Late Feeding.
Mentions: With earlier on-shore arrival, substantial declines in mean litter size (X) are predicted for both feeding scenarios (Fig. 3). With Early Feeding, we predict X=1.05 if bears come ashore on 1 July and X=0.75 for on-shore arrival on 1 June. Predicted declines are stronger with Late Feeding, with X=0.45 for on-shore arrival on 1 July and no reproduction (X=0) for on-shore arrival before 7 June. For both scenarios, we predict the proportions of females with twins and triplets to decline monotonically and the proportion of non-reproducing females to increase monotonically (Fig. 3a,b). Declines in twin and triplet production will precede declines in the proportion of females having singletons, because some females will move from having twins to having singletons, whereas others will move from having singletons to not reproducing. These predicted changes are consistent with patterns already observed in western Hudson Bay where females are now forced ashore 1–2 weeks earlier than during the early 1990s, and both body condition and reproduction have declined711. More precise data suitable for model validation do not exist, and it is noteworthy in this regard that the predicted litter size changes will be difficult to document if monitoring focuses on X* rather than on X (Fig. 3c,d).

Bottom Line: In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40-73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55-100% if break-up occurs 2 months earlier.Simultaneously, mean litter size would decrease by 22-67% and 44-100%, respectively.Similar litter size declines may occur in over one-third of the global polar bear population.

View Article: PubMed Central - PubMed

Affiliation: Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2G1. pmolnar@ualberta.ca

ABSTRACT
Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40-73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55-100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22-67% and 44-100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population.

Show MeSH
Related in: MedlinePlus