The polar bear (Ursus maritimus) is a marine mammal that inhabits the circumpolar Arctic, spending most of its life on the sea ice. These massive carnivores are adapted to their frozen environment, where they hunt and raise their young. The importance of the polar bear extends beyond its physical presence, influencing the Arctic ecosystem and providing scientists with unique data.
The Polar Bear’s Role as an Apex Predator
Polar bears sit at the top of the Arctic food web, functioning as the region’s apex predator. Their diet consists almost entirely of seals, particularly ringed and bearded seals, which they hunt on the sea ice. By preying on these species, the bears help regulate seal populations, preventing overpopulation that could destabilize lower trophic levels, such as fish and krill.
Their hunting behavior creates a crucial link between the marine and terrestrial environments. When a polar bear consumes a seal, it typically eats the fat-rich blubber but often leaves significant portions of the carcass on the ice. This carrion provides a necessary food source for Arctic scavengers, including the Arctic fox and ravens. Researchers estimate that polar bears leave behind millions of kilograms of prey annually, transferring ocean energy to the ice surface for other animals to access.
A Barometer for Global Climate Health
Polar bears are considered an indicator species because their survival is tied to the stability of the sea ice. They rely on this frozen platform for traveling, mating, and ambushing the seals that are their primary food source. Monitoring the health and population trends of Ursus maritimus offers a quantifiable measure of the speed and severity of Arctic warming.
The decline in sea ice is directly linked to the polar bear’s ability to hunt, forcing them to spend longer periods on land where they must fast. Data collected in areas like Western Hudson Bay has demonstrated a link between climate-driven sea ice loss and population decline, with one subpopulation halving over four decades due to reduced hunting opportunities. Trends show that the period of ice-covered days is declining across all 19 polar bear subpopulations, with sea-ice retreat occurring earlier and the advance occurring later. This measurable shift provides scientists with long-term evidence of climate change consequences.
Scientific Insights from Unique Physiology
The polar bear’s specialized biology offers scientific insights with potential applications for human health research. These animals subsist on a diet that is up to 50% fat, yet they avoid the arterial plaques and cardiovascular diseases that afflict humans with similar high-fat diets. Genetic analysis has revealed evolutionary adaptations in genes related to fat transport and cardiovascular function.
One strongly selected gene is APOB, which in humans encodes the main protein in low-density lipoprotein, or “bad” cholesterol. The polar bear’s variant of this gene allows them to cope with high levels of cholesterol and triglycerides without developing heart conditions. Studying these genetic mechanisms provides a pathway for managing human conditions like obesity and cardiovascular disease. Furthermore, their ability to gain weight seasonally and then enter a hibernation-like fasting state without suffering bone density loss or muscle atrophy offers clues for treating human ailments related to prolonged immobility.