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Polar bear


Global warming will have far reaching effects on the Arctic ecosystem.

The area of pack ice will decrease with potentially disastrous effects for Arctic species like polar bears which are entirely dependent on pack ice.

The Arctic


hd: The Fragile web of life
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Arctic ecosystems are characterized by complex interrelationships between species and their physical environment. The life of a particular species is an intricate tapestry of land and ice conditions, seasonal changes, and interdependencies on other plants and animals. As a result, climate-induced changes that affect one part of a species life cycle can have wide-reaching effects on the ecosystem as a whole. This inter-relationship is clearly demonstrated by the polar bear and its principal prey, the ringed seal-both produce their young in the shelter of snow caves and thus are highly dependent on snow conditions.

Polar bears require deep snow, and their denning across the Arctic is strongly influenced by the availability of snow drifts. Although ringed seals do not require as deep snow as polar bears, their success in raising young is critically dependent on the integrity of the snow cave. The young born on top of the ice in the spring have a protective wool coat, but do not yet have a protective layer of blubber. As a result, they cannot withstand the extreme conditions outside of the snow caves. Unseasonal warming at the southern edge of the snow pack can lead to collapses of the snow caves, and the exposed young are rendered helpless when bitter cold returns. Scientists suspect that the systematic warming in the Arctic, manifested by more frequent bouts of warm weather, will lead to more collapsed caves, and ultimately to a reduction of area suitable for seal denning.

For polar bears, the effect of this systematic warming will be indirect, but serious. A decline in seal prey will result in an inevitable decline in polar bear populations. Adult polar bears near Churchill, Manitoba, fast during the summer and early fall, when they are forced to stay on land because of the lack of sea ice. Incredibly, females fast for seven to eight months, leaving the ice early in the spring to den on land. With the return of ice in the fall, the bears immediately move out onto Hudson¹s Bay to begin the winter season of hunting. Any decrease in the abundance of seal prey or in the length of time the ocean is ice-covered can be expected to have devastating effects on this most southern of populations. Recent evidence indicates that changes may already be underway. Biologists have noted a decline in birth rates and suspect that the average physical condition of adult bears is worsening.

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