Dietary ecology of Alaskan polar bears (Ursus maritimus) through time and in response to Arctic climate change. (1st April 2021)

• Record Type: Journal Article
• Authors: Petherick, Ansley S.; Reuther, Joshua D.; Shirar, Scott J.; Anderson, Shelby L.; DeSantis, Larisa R. G.
• Is Part Of: Global change biology. Volume 27:Number 13(2021)
• Page Start: 3109
• Page End: 3119
• Publication Date: 2021-04-01
• Subjects: archaeology -- Carnivora -- dental microwear -- diet -- mammal -- ursid -- Ursus arctos; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15573
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Arctic climate change poses serious threats to polar bears ( Ursus maritimus ) as reduced sea ice makes seal prey inaccessible and marine ecosystems undergo bottom‐up reorganization. Polar bears' elongated skulls and reduced molar dentition, as compared to their sister species the grizzly bear ( Ursus arctos ), are adaptations associated with hunting seals on sea ice and a soft, lipid‐rich diet of blubber and meat. With significant declines in sea ice, it is unclear if and how polar bears may be altering their diets. Clarifying polar bear dietary responses to changing climates, both today and in the past, is critical to proper conservation and management of this apex predator. This is particularly important when a dietary strategy may be maladaptive. Here, we test the hypothesis that hard‐food consumption (i.e., less preferred foods including bone), inferred from dental microwear texture analysis, increased with Arctic warming. We find that polar bears demonstrate a conserved absence of hard‐object feeding in Alaska through time (including approximately 1000 years ago), until the 21st century, consistent with a highly conserved and specialized diet of soft blubber and flesh. Notably, our results also suggest that some 21st‐century polar bears may be consuming harder foods (e.g., increased carcass utilization, terrestrial foods including garbage), despite having skulls and metabolisms poorly suited for such a diet. Prior to the 21st century, only polar bears with larger mandibles demonstrated increased hard‐object feeding, though to a much lower degree than closely related grizzly bears which regularly consume mechanically challenging foods. Polar bears, being morphologically specialized, have biomechanical constraints which may limit their ability to consume mechanically challenging diets, with dietary shifts occurring only under the most extreme scenarios. Collectively, the highly specialized diets and cranial morphology of polar bears may severely limit their ability to adapt to a warming Arctic. Abstract : Polar bears ( Ursus maritimus ) are specialist predators which are threatened by Arctic warming and sea ice decline. This study uses dental microwear texture analysis to investigate polar bear feeding ecology during past and present climate change. We find that polar bears have consumed a highly conserved diet of soft foods (e.g., blubber and flesh) through time, including during a previous period of Arctic warming (i.e., the Medieval Warm Period); however, some 21st‐century Alaskan polar bears consume significantly harder diets (e.g., bone) in response to warming climates—a diet which they are poorly adapted to consume.