Polar bears experience skeletal muscle atrophy in response to food deprivation and reduced activity in winter and summer

Whiteman, John P.; Harlow, Henry J.; Durner, George M.; Regehr, Eric V.; Rourke, Bryan C.; Robles, Manuel; Amstrup, Steven C.; Ben‐David, Merav

doi:10.1093/conphys/cox049

Cited by 16 publications

(16 citation statements)

References 97 publications

(126 reference statements)

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“…Bears hunt seals throughout the ice-covered season and during spring have a hyperphagic period when ringed seal pups are abundant. A portion of the energy obtained during this period is converted to fat stores that are subsequently used during the icefree season while bears are fasting or have restricted access to food , Wiig et al 2008, Stirling & Derocher 2012, Whiteman et al 2017. Thus, the timing and availability of sea ice has significant impact on body condition and reproduction (Rode et al 2012(Rode et al , 2014, and ultimately survival of polar bears (Regehr et al 2007, Lunn et al 2016.…”

Section: Introductionmentioning

confidence: 99%

Changes in winter and spring resource selection by polar bears Ursus maritimus in Baffin Bay over two decades of sea-ice loss

Laidre¹,

Stern²,

Born³

et al. 2018

Endang. Species. Res.

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Loss of Arctic sea ice has implications for the distribution and population structure of ice-dependent species such as polar bears Ursus maritimus. We used remotely sensed sea-ice concentration data for Baffin Bay, Canada, and satellite telemetry for adult female polar bears in the 1990s (n = 43) and 2000s (n = 38) to assess whether sea-ice habitat changes have influenced movements and habitat selection. Both the timing and availability of sea-ice habitat changed significantly between the 1990s and 2000s. Mean sea-ice concentration in June−October declined from 22 to 12%. Spring sea-ice retreat occurred 2 wk earlier and fall sea-ice advance 2 wk later in the 2000s. These changes translated directly to changes in habitat use by polar bears. In the 2000s, bears used significantly lower sea-ice concentrations in winter and spring. Also, bears were significantly closer to land in all months, except at the end of spring breakup when they remained on offshore sea ice as long as possible, likely to maximize foraging time prior to coming on land where they are largely food deprived. The presence of summer offshore sea ice facilitated broad movement of bears in the 1990s; however, this ice disappeared in the 2000s and resulted in significant declines in monthly movement rates. In the 2000s, adult females selected for lower sea-ice concentrations if they facilitated access to the continental shelf (< 300 m). Our findings indicate that significant changes in available sea-ice habitat and habitat use in Baffin Bay have occurred since the mid-1990s and this subpopulation will likely experience negative population-level impacts related to a changing climate in the coming decades. In some other parts of the Arctic, such changes have preceded negative nutritional and demographic impacts.

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Section: Introductionmentioning

confidence: 99%

Changes in winter and spring resource selection by polar bears Ursus maritimus in Baffin Bay over two decades of sea-ice loss

Laidre¹,

Stern²,

Born³

et al. 2018

Endang. Species. Res.

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“…However, the amount of digestible energy available to polar bears from subsistence‐harvested bowhead whale carcasses on land is currently unknown. While these whale carcasses appear to energetically benefit the current number of polar bears on land (Whiteman et al 2017 a ), it is unknown how many additional bears could be supported. Competition with grizzly bears ( U. arctos ) at these sites may further limit the number of polar bears that could benefit energetically from these carcasses (Miller et al ).…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, the number of land bears has been found to be influenced by sea ice conditions with more bears using land in years of greater ice retreat (Schliebe et al , Wilson et al ), which suggests an energetic tradeoff depending upon annual ice conditions. Whiteman et al (2017 a ) documented muscle atrophy in SB ice bears, while SB land bears lacked such atrophy. This suggested that ice bears were feeding less (primarily fasting) and had reduced activity relative to land bears (Whiteman et al 2017 a ).…”

Section: Introductionmentioning

confidence: 99%

“…Whiteman et al (2017 a ) documented muscle atrophy in SB ice bears, while SB land bears lacked such atrophy. This suggested that ice bears were feeding less (primarily fasting) and had reduced activity relative to land bears (Whiteman et al 2017 a ). This, in turn, would indicate little energetic benefit in remaining on the summer sea ice as it retreats beyond the continental shelf.…”

Section: Introductionmentioning

confidence: 99%

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The seasonal energetic landscape of an apex marine carnivore, the polar bear

Pagano

Atwood

Durner

et al. 2020

Ecology

Self Cite

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Divergent movement strategies have enabled wildlife populations to adapt to environmental change. In recent decades, the Southern Beaufort Sea subpopulation of polar bears (Ursus maritimus) has developed a divergent movement strategy in response to diminishing sea ice where the majority of the subpopulation (73–85%) stays on the sea ice in summer and the remaining bears move to land. Although declines in sea ice are generally considered a challenge to energy balance in polar bears residing in some regions of the Arctic, little quantitative data exists concerning the seasonal energy expenditures of this apex marine carnivore. We used GPS satellite collars with tri‐axial accelerometers and conductivity sensors to measure the location, behavior, and energy expenditure of five adult female polar bears in the southern Beaufort Sea across seasons of sea ice breakup and minimum extent. Using a Bayesian mixed‐effects model, we found that energy expenditure was influenced by month, ocean depth, and habitat type (sea ice or land). Total energy expenditure from May through September ranged from 37.7 to 47.2 mJ/kg for individual bears. Bears that moved to land expended 7% more energy on average from May through September than bears that remained on the receding sea ice. In August, when bears were moving from the sea ice to land or moving north with the receding pack ice, bears that moved to land spent 7% more time swimming and expended 22% more energy. This means the immediate cost of moving to land exceeded the cost of remaining on the receding summer pack ice. These findings suggest a physiological reason why the majority of the Southern Beaufort Sea subpopulation continues to inhabit a diminishing summer ice platform. However, bears that moved to land spent 29% more time in preferred hunting habitats over the continental shelf than bears that remained on the sea ice. Bears on land also had access to subsistence‐harvested bowhead whale carcasses. Hence, our findings indicate there may be a greater overall energetic benefit to move to land in this region, which suggests that the use of the diminishing summer sea ice may be functioning as an ecological trap.

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“…For instance, the mosaic-tailed rat Melomys rubicola became apparently the first species whose extinction occurred as a result of habitat destruction due to sea level rise (Gynther et al 2016). For the same reason polar bears (Ursus maritimus) face starvation and experience muscle atrophy and weight loss (Obbard et al 2016a,b;Whiteman et al 2017;Pagano et al 2018). For hunting, this species relies on sea ice, where seals, their primary source of food, rest and breed.…”

Section: Introductionmentioning

confidence: 99%

Evolutionary dynamics and diversification in changing environments

Alekseeva

Doebeli

Ispolatov

2019

Preprint

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We use adaptive dynamics models to study how changes in the abiotic environment affect patterns of evolutionary dynamics and diversity in evolving communities of organisms with complex phenotypes. The models are based on the logistic competition model and environmental changes are implemented as a temporal change of the carrying capacity as a function of phenotype. We observe that the rate of environmental change is a crucial factor that determines whether the community survives or undergoes extinction. Surviving communities adapt to the changing conditions and converge to new stationary states, producing a diverse spectrum of evolutionary dynamics. In the majority of surviving systems we observe a reduction in the number of species, total population size and phenotypic diversity. However, for some systems with initially low number of species, slow environmental changes appear to be a driver of speciation and generate communities with higher phenotypic diversity. Phenotypes of surviving species generally evolve in the direction of the moving maximum of the carrying capacity. However, species also evolve in various phenotypic directions orthogonal to the motion of the optimum. The intensity of this undirected phenotypic dynamics increases with the rate of environmental changes. AbstractWe use adaptive dynamics models to study how changes in the abiotic environment affect patterns of evolutionary dynamics and diversity in evolving communities of organisms with complex phenotypes. The models are based on the logistic competition model and environmental changes are implemented as a temporal change of the carrying capacity as a function of phenotype. We observe that the rate of environmental change is a crucial factor that determines whether the community survives or undergoes extinction. Surviving communities adapt to the changing conditions and converge to new stationary states, producing a diverse spectrum of evolutionary dynamics. In the majority of surviving systems we observe a reduction in the number of species, total population size and phenotypic diversity. However, for some systems with initially low number of species, slow environmental changes appear to be a driver of speciation and generate communities with higher phenotypic diversity. Phenotypes of surviving species generally follow the moving maximum of the carrying capacity. However, species also evolve in various phenotypic directions relative to the motion of the optimum. The intensity of this undirected phenotypic dynamics increases with the rate of environmental changes.

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Polar bears experience skeletal muscle atrophy in response to food deprivation and reduced activity in winter and summer

Cited by 16 publications

References 97 publications

Changes in winter and spring resource selection by polar bears Ursus maritimus in Baffin Bay over two decades of sea-ice loss

Changes in winter and spring resource selection by polar bears Ursus maritimus in Baffin Bay over two decades of sea-ice loss

The seasonal energetic landscape of an apex marine carnivore, the polar bear

Evolutionary dynamics and diversification in changing environments

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