Polar bear
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| Polar Bear | ||||||||||||||||
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| Ursus maritimus Phipps, 1774[2] | ||||||||||||||||
 Polar bear range | ||||||||||||||||
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| Ursus eogroenlandicus |
The polar bear (Ursus maritimus) is a bear native largely within the Arctic circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest carnivore species found on land. It is also the largest bear, together with the omnivore Kodiak bear which is approximately the same size.[3] An adult male weighs around 350–680 kg (770–1,500 lb),[4] while an adult female is about half that size. Although it is closely related to the brown bear, it has evolved to occupy a narrow ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet.[5] Although most polar bears are born on land, it spends most of its time at sea, hence its name meaning "maritime bear", and can hunt consistently only from sea ice, spending much of the year on the frozen sea.
The polar bear is classified as a vulnerable species, with 5 of the 19 polar bear subpopulations in decline.[6][7] For decades, unrestricted hunting raised international concern for the future of the species; populations have rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and the hunting of polar bears remains important in their cultures.
The IUCN now lists global warming as the most significant threat to the polar bear, primarily because the melting of its sea ice habitat reduces its ability to find sufficient food. The IUCN states, "If climatic trends continue polar bears may become extirpated from most of their range within 100 years."[1] On May 14, 2008, the United States Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act.
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Naming and etymology
Constantine John Phipps was the first to describe the polar bear as a distinct species.[1] He chose the scientific name Ursus maritimus, the Latin for 'maritime bear',[8] due to the animal's native habitat. The Inuit refer to the animal as nanook,[9] (transliterated as nanuuq in the Inupiaq language,[10] and nanuuk in Siberian Yupik.[citation needed]) The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear").[11] In Quebec French, the polar bear is referred to as Ours polaire.[12] In the Norwegian administered Svalbard archipelago, the polar bear is referred to as Isbjørn ("ice bear").
The polar bear was previously considered to be in its own genus, Thalarctos.[13] However, evidence of hybrids between polar bears and brown bears, and of the recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.[14]
Taxonomy and evolution
The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear, Ursus arctos, roughly 200,000 years ago. The oldest known polar bear fossil is less than 100,000 years old. Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.[15]
More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears,[16] meaning that the polar bear is not a true species according to some species concepts.[17] In addition, polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids,[15][18] indicating that they have only recently diverged and are genetically similar.[19] However, as neither species can survive long in the other's ecological niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.[19]
When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776.[20] This distinction has since been invalidated.
One fossil subspecies has been identified. Ursus maritimus tyrannus—descended from Ursus arctos—became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.[15]
Population and distribution
The polar bear is found throughout the Arctic Circle and adjacent land masses . Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore.[21] While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south as Berlevåg on the Norwegian mainland and the Kuril Islands in the Sea of Okhotsk. It is difficult to estimate a global population of polar bears as much of the range has been poorly studied, however biologists use a working estimate of about 20,000-25,000 polar bears worldwide.[6]
There are 19 generally recognized discrete subpopulations.[6][7] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated.[22] The thirteen North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to Baffin Bay in western Greenland and account for about 70% of the global population. The Eurasian population is broken up into the eastern Greenland, Barents Sea, Kara Sea, Laptev Sea, and Chukchi Sea subpopulations, though there is considerable uncertainty about the structure of these populations due to limited mark and recapture data.
The range includes the territory of five nations: Denmark (Greenland), Norway (Svalbard), Russia, US (Alaska) and Canada. These five nations are the signatories of the 1973 International Agreement for the Conservation of Polar Bears, which mandates cooperation on research and conservations efforts throughout the polar bear's range.
Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area.[23] The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear.[23] In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are.[23] The Polar Bear Specialist Group of the IUCN takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies."[24]
Of the 19 recognized polar bear subpopulations, 8 are declining, 3 are stable, 1 is increasing, and 7 have insufficient data.[6][7
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