Dietary ecology of Alaskan polar bears (Ursus maritimus) through time and in response to Arctic climate change

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.

Polar bear diet in the face of Arctic climate change

“…Putting these polar bear characteristics into context, findings reported by Petherick et al (2021) are consistent with a scenario where hard-food consumption by Alaskan polar bears remained low throughout historical times despite fluctuations in Arctic temperatures from 1000 years ago to the end of the 20th century. The lack of a significant hard-food signal in DMTA data in pre-21st century polar bear dental enamel suggests a history of feeding ecology that operated within the bounds of polar bear skull functional morphology (Slater et al, 2010).…”

“…The pole-warming effects of ongoing climate change and the position of polar bears (Ursus maritimus) as top predators of the Arctic ecosystem meet at a precarious nexus, making this large mammal a modern day "canary in the mine." Petherick et al (2021) take a pulse of polar bear diet by examining key signatures in the microscopic attritional patterns on the surface of polar bear dental enamel.…”

“…One such tool is dental microwear texture analysis (DMTA), used by Petherick et al (2021) to quantify dietary signatures on polar bear dental enamel to test hypotheses about their dietary shifts through time. Dental enamel microwear methodology has its roots in mammalian herbivore dietary analysis (Walker et al, 1978).…”

What's going to be on the menu with global environmental changes?

“…Dental microwear texture analysis (DMTA): Wear to tooth enamel acquired from food processing may be recorded using scanning microscopy and used to assess dietary behavior (Calandra & Merceron, 2016). Relatively nuanced details on food texture and feeding ecology may be inferred, more frequently with specimens in natural history collections (Bestwick et al, 2020;Petherick et al, 2021) but also noninvasively with the shed teeth of living animals (McLennan…”

Contribution of hybridization between polar bears and grizzly bears to polar bear extinction

“…Polar bear feeding habits on land have been well documented. We know that the polar bear's diet is changing (Petherick et al, 2021). During their stay on land, polar bears have consumed blueberries ( Vaccinium wiginosum ), moss, lichens, seaweed, snow geese ( Anser caerulescens ), thick‐billed murre ( Uria lomvia ), small rodents, human garbage, and they scavenged on bowhead whales ( Balaena mysticetus ) (Derocher, Andriashek, et al, 1993; Derocher, Wiig, 2000; Laidre, Born, et al, 2018; Laidre, Stirling et al (2018); Rockwell & Gormezano, 2009; Russell, 1975; Smith et al, 2010).…”