The world’s largest bear, the polar bear lives in arctic regions of the United States, Canada, Russia, Greenland, and Norway. Polar bear habitat refers to the unique combination of biotic and abiotic factors that affect successful survival and propagation of polar bears. Biotic factors, or biological influences, include the entire array of living organisms, or the ecological community. Abiotic factors are the physical, or nonliving, factors, such as climate and nutrient availability. These factors relate to the geographic range of the organism.
The availability of the polar bear's primary and secondary food sources, ringed seals and bearded seals, dominates the polar bear habitat. By some estimates, polar bears kill up to 44% of newborn ringed seal pups in the spring, a time when young bear cubs are gaining weight at the rate of a pound (500 grams) a day. Bearded seals are larger than ringed seals and pose a greater challenge. Polar bears do not digest plant material well and need a high ratio of fat and protein in their diets. A seal, with its fat layer that protects it from the cold, is ideally suited as the polar bear’s main food source.
Another biotic factor of polar bear habitat is the fish populations upon which seals feed. These fish will vary depending on their habitat’s biotic and abiotic factors. Biotic factors include density of small animals and micro-organisms. Water temperature and oxygen content are examples of abiotic factors. Thus, the entire food chain of the arctic ecology becomes a factor in the polar bear habitat, making polar bears the top of their food chain.
The habitat of polar bears also reflects the abiotic factors of climate and local weather. Polar bears migrate with the melting and freezing of sea ice, just as the air-breathing seals do. While the climate largely depends on latitude, shape of the coastline and presence of islands, coves, and inlets influence the local ebb and flow of sea ice.
The northern range of these animals exposes them to a high level of ultraviolet light (UV), an abiotic factor. It was once believed that the fur transported UV to the skin for absorption. Subsequent studies discounted that theory, although the bear’s fur absorbs UV light, protecting the skin. Polar bear skin is black, perhaps to increase heat retention.
Pregnant females form dens, usually on land, but males and non-pregnant females live primarily on the sea ice year-round. The preferred habitat is sea ice near the shore that accommodates hunting and den-making needs. Weather dictates the time when pregnant females form dens. Drifts of snow must be deep and permanent enough to house a snow cave. The bears do not dig into the earth below the snow and ice.
Hunting by humans for food, fur, or as trophies has been a factor in polar bear habitat for centuries, beginning with early Eurasian explorers. During the late 1800s through the early 1900s, hunting of these bears devastated some populations. Hunting continued, to a lesser degree, through the 1950s. In 1976, the five countries with polar bear habitat signed the International Agreement on Conservation of Polar Bears. The treaty banned hunting from aircraft or large motorized vessels and initiated other protective measures.