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 - 47.2 mJ kg-1 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. Meaning 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.

中文翻译：

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顶级海洋食肉动物北极熊的季节性活力景观

不同的运动策略使野生动物种群能够适应环境变化。近几十年来，南波弗特海北极熊亚种群 (Ursus maritimus) 制定了一种发散运动策略，以应对海冰减少，其中大多数亚种群 (73-85%) 在夏季停留在海冰上，其余的熊搬到陆地上。尽管海冰减少通常被认为是对居住在北极某些地区的北极熊能量平衡的挑战，但关于这种顶级海洋食肉动物的季节性能量消耗的定量数据很少。我们使用带有三轴加速度计和电导率传感器的 GPS 卫星项圈来测量位置、行为、波弗特海南部五只成年雌性北极熊在海冰破裂季节和最小范围内的能量消耗。使用贝叶斯混合效应模型，我们发现能量消耗受月份、海洋深度和栖息地类型（海冰或陆地）的影响。从 5 月到 9 月，单个熊的总能量消耗为 37.7 - 47.2 mJ kg-1。从 5 月到 9 月，迁移到陆地的熊比留在消退的海冰上的熊平均多消耗 7% 的能量。8 月，当熊从海冰迁移到陆地或随着浮冰的消退向北移动时，迁移到陆地的熊游泳时间增加了 7%，消耗的能量增加了 22%。这意味着搬到陆地的直接成本超过了留在消退的夏季浮冰上的成本。这些发现表明了为什么大多数南波弗特海亚种群继续居住在逐渐减少的夏季冰平台上的生理原因。然而，与留在海冰上的熊相比，迁移到陆地的熊在大陆架上首选的狩猎栖息地中花费的时间多 29%。陆地上的熊也可以接触到自给自足的弓头鲸尸体。因此，我们的研究结果表明，迁移到该地区的陆地可能会带来更大的整体能量收益，这表明利用夏季减少的海冰可能起到了生态陷阱的作用。与留在海冰上的熊相比，搬到陆地上的熊在大陆架上首选的狩猎栖息地中花费的时间多 29%。陆地上的熊也可以接触到自给自足的弓头鲸尸体。因此，我们的研究结果表明，迁移到该地区的陆地可能会带来更大的整体能量收益，这表明利用夏季减少的海冰可能起到了生态陷阱的作用。与留在海冰上的熊相比，搬到陆地上的熊在大陆架上首选的狩猎栖息地中花费的时间多 29%。陆地上的熊也可以接触到自给自足的弓头鲸尸体。因此，我们的研究结果表明，迁移到该地区的陆地可能会带来更大的整体能量收益，这表明利用夏季减少的海冰可能起到了生态陷阱的作用。