Tuesday, November 6, 2012

The polar bear


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 land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size.[3] A boar (adult male) weighs around 350–680 kg (770–1,500 lb),[4] while a sow (adult female) is about half that size. HP Compaq HSTNN-105C Battery

Although it is closely related to the brown bear, it has evolved to occupy a narrower 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, they spend most of their time at sea. HP Compaq HSTNN-C12C Battery

Their scientific name means "maritime bear", and derives from this fact. Polar bears can hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present.

The polar bear is classified as a vulnerable species, with eight of the nineteen polar bear subpopulations in decline.[6]HP Compaq HSTNN-C66C Battery

For decades, large scale hunting raised international concern for the future of the species but populations 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 polar bears remain important in their cultures.

Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774.[7] HP Compaq HSTNN-C66C-4 Battery

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 nanuq in the Inupiat language).[10] TheYupik also refer to the bear as nanuuk in Siberian Yupik.[11] The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), HP Compaq HSTNN-C66C-5 Battery

though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear").[12] In French, the polar bear is referred to as ours blanc ("white bear") or ours polaire ("polar bear").[13] 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.[14] HP Compaq HSTNN-C67C Battery

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 thereforeUrsus maritimus, as Phipps originally proposed.

The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. HP Compaq HSTNN-C67C-4 Battery

The Ursinae subfamily originated approximately 4.2 million years ago. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004.[16] 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.[17] HP Compaq HSTNN-C67C-5 Battery

The evidence from DNA analysis is more complex. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear,Ursus arctos, roughly 150,000 years ago.[16] Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears,[18] meaning that the polar bear would not be a true species according to some species concepts.[19] HP Compaq HSTNN-DB05 Battery

The mtDNA of Irish brown bears is particularly close to polar bears.[20] A comparison of thenuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago,[21] although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar, HP Compaq HSTNN-DB06 Battery

brown and black bears, and establishes the divergence of polar and brown bears at 4-5 million years ago.[22]

However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land and brown bears migrated northward. Most brown bears have about 2 percent genetic material from polar bears, HP Compaq HSTNN-DB0E Battery

but one population residing in the Alexander Archipelago has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating. Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar.[23] HP Compaq HSTNN-DB11 Battery

However, because neither species can survive long in the other's ecological niche, and because they have differentmorphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.[25]

When the polar bear was originally documented, two subspecies were identified: HP Compaq HSTNN-DB16 Battery

Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776.[26] 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. HP Compaq HSTNN-DB28 Battery

The polar bear is found in the Arctic Circle and adjacent land masses as far south as Newfoundland Island. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore.[27] 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 Bayin Canada. HP Compaq HSTNN-DB29 Battery

They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south asBerlevåg 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 to 25,000 polar bears worldwide. HP Compaq HSTNN-DB67 Battery

There are 19 generally recognized, discrete subpopulations.[28][29] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated.[30] 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. HP Compaq HSTNN-FB05 Battery

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, the United States (Alaska) and Canada. HP Compaq HSTNN-FB18 Battery

These five nations are the signatories of the International Agreement on 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.[31] HP Compaq HSTNN-FB51 Battery

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.[31] In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. HP Compaq HSTNN-FB52 Battery

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