Determining the future of polar bears in a warming world Understanding the occurrence and cost benefit of terrestrial foraging and the implications of increased land use

北极熊生活在漂浮在北冰洋上的海冰上，这些海冰每年在加拿大东部的海湾和岛屿之间形成和融化。这个海冰栖息地为北极熊提供了一条接近海豹的途径，海豹是它们的主要猎物。北极熊捕食海豹，它们会在冰面上的洞里呼吸，也会把海豹拖到冰面上生孩子。海豹的脂肪是整个北极北极熊的主要能量来源。不断变化的北极气候已经减少了北极熊可以用来接近海豹的海冰数量，而在未来100年里，气温持续上升几度，预计北极许多地区夏季和初秋的海冰将进一步减少。随着冰层的减少，北极熊在北极大部分地区花更多的时间在陆地上，而它们无法接触到海豹。虽然人们观察到北极熊以筑巢的鹅和海鸟、浆果和植被为食，但这些食物比北极熊的典型猎物更分散，能量更少。因此，陆地食物的质量、数量和分布可能都不足以保证目前北极熊的广泛分布。这项研究旨在更好地了解北极熊在陆地上的行为，以及陆地食物在多大程度上满足了北极熊的能量需求。北极熊是在陆地上长时间失去体重还是保持体重，这个问题对于确定海冰减少对出生率和死亡率的潜在影响至关重要——大多数北极国家都需要这些信息来管理他们的北极熊。由于北极熊处于北极食物链的顶端，它们也是北极变化的关键指示物种，也是气候变化影响的标志性象征。我们的研究结果将有助于确定进一步保护这一物种的行动，以及其文化和安全与这种北极捕食者的行为密切相关的社区。这项研究的目的是确定北极熊在陆地上避暑时的行为和能量平衡。我们建议：1)量化在陆地上消耗的食物在多大程度上满足北极熊的能量需求；2)由此提供必要的信息，以了解北极地区气候变暖、海冰融化和土地利用对北极熊健康和种群动态的影响。我们将通过测量能量消耗，体重变化，脂肪和蛋白质组成的体重变化，活动和运动率，以及雄性和雌性，年轻的和年老的进食行为来做到这一点。我们将用双标记同位素水测量的能量消耗与身体脂肪和蛋白质被动员时释放的能量之间的差异来估计来自食物的能量。如果这些值相等，则没有有用的能量来自食物。如果用双标记水测量的能量消耗高于从动员的蛋白质和脂肪中获得的能量消耗，那么这个差异就是来自摄入食物的能量。这些测量只能用人类和动物研究中最先进的技术来完成。这些技术包括：1)内置摄像头的GPS项圈，可以让我们准确跟踪熊的活动，直接观察它们在做什么和吃什么；2)同位素水稀释技术，可以测量它们燃烧的卡路里数量，以及它们在两次捕获之间增加或减少了多少脂肪和蛋白质，这两次捕获间隔大约21天。这些技术将使我们能够确定北极熊越来越多地使用陆地的影响，因为它们的海冰栖息地继续减少。因此，这项研究将为了解北极熊种群的未来提供信息，北极熊是北极食物网的重要组成部分，在变暖的北极。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Polar bears live on sea ice that floats over the Arctic Ocean and that forms and melts each year within bays and among islands in eastern Canada. This sea ice habitat is critical for providing polar bears a way to access seals, their primary prey. Polar bears hunt seals where they come up to breathe at holes in the ice and when they haul out onto the ice to have their pups. The blubber of seals is the primary energy source for polar bears throughout the Arctic. A changing Arctic climate has already reduced the amount of sea ice that bears can use to access seals, and continued warming of several degrees over the next 100 years is expected to further decrease sea ice during the summer and early fall in many parts of the Arctic. With less ice, polar bears across much of the Arctic are spending more time on land where they cannot access seals. Although polar bears have been observed feeding on nesting geese and seabirds, berries, and vegetation, these foods are more disbursed and less-energy rich than the typical prey of polar bears. Thus, land-based foods may not occur in sufficient quality, quantity, or distribution to ensure the current widespread distribution of polar bears. This study seeks to better understand bear behavior on land and the degree to which land-based foods meet the energetic needs of polar bears. The question of whether bears lose or maintain their body mass for extended periods on land is critical to determining potential effects of sea ice loss on birth and death rates – information that most Arctic nations need to manage their resident polar bears. Because polar bears occur at the top of the Arctic food chain, they are also a key indicator species for changes in the Arctic as well as an iconic symbol of the effects of a changing climate. Our results will help identify actions to further protect this species and the communities whose cultures and safety are closely linked to the behavior of this Arctic predator.The goals of this study are to determine the behavior and energetic balances of polar bears while summering on land. We are proposing to 1) quantify the degree to which foods consumed while on land meet the energetic needs of polar bears and 2) thereby provide the information necessary to understand the implications of increasing warming, sea ice loss, and land use on polar bear well-being and population dynamics across the Arctic. We will do this by measuring energy expenditure, weight change, fat and protein composition of the weight change, activity and movement rates, and feeding behavior of males and females, young and old while they are on land. We will estimate the amount of energy coming from food as the difference between the energy expenditure measured with doubly labeled isotopic water and the energy released when body fat and protein are mobilized. If these values are equal, no useful energy is coming from food. If the energy expenditure measured with doubly labeled water is higher than that available from mobilized protein and fat, then that difference is the amount of energy coming from ingested food. These measurements can only be done with the most advanced techniques available for human and animal research. These techniques include 1) GPS collars with built in video cameras that will allow us to accurately track bear movements and directly observe what they are doing and eating and 2) an isotopic water dilution technique that allows measurement of the number of calories they burn and how much fat and protein they gain or lose between two captures which will be about 21 days apart. These techniques will allow us to determine the implications of polar bears increasingly using land as their sea ice habitat continues to decline. Thus, this study will provide information for understanding the future of polar bear populations, a significant part of Arctic food web, in a warming Arctic.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.