Ursus Maritimus

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in biology, polar bear (Alias:Ursus maritimus) It is an animal in the family Ursidae and the genus Ursus. It is the largest terrestrial carnivore in the world, also known as the white bear. The polar bear is the largest extant species of bear and land carnivore, with adult males weighing 300–800 kg (660–1,760 lb). The species is sexually dimorphic, as adult females are much smaller. The polar bear is white- or yellowish-furred with black skin and a thick layer of fat. It is more slender than the brown bear, with a narrower skull, longer neck and lower shoulder hump. Its teeth are sharper and more adapted to cutting meat. The paws are large and allow the bear to walk on ice and paddle in the water.

Polar bears live in the ice-covered waters of the Arctic Circle. Winter burrows can reach depths reaching the permafrost. The preferred habitat is the ice floes of the Arctic Ocean. Ice edges and pressure ridges where breakup and refreezing occur provide the best hunting grounds. Generally solitary, except during mating and lactation periods. Approximately 66.6% of the time during most of the year is inactive, with the remaining time 29.1% spent walking and swimming, stalking prey 1.2%, or eating 2.3%. Polar bears are excellent swimmers and may search for food over a wide range. It is the most carnivorous species, with 98.5% of its food being meat. The main prey are seals and even larger species such as walruses and beluga whales. It also preys on seabirds, fish, and small mammals, and sometimes scavenges carrion. In summer they occasionally eat berries or plant roots. At the end of spring and summer, people will also go to the beach to pick up washed seaweed to replenish the minerals and vitamins needed by the body.

Polar bears are found throughout the ice-covered waters of the Arctic Circle. In areas where Arctic sea ice melts completely each summer, polar bears are forced to spend several months on land, where they feed primarily on stored fat until the sea freezes.

Classification

Phipps first described the polar bear as a separate species in 1774, naming it "Ursus maritimus." Other suggested synonyms include "Thalassarctos," "Thalarctos," and "Thalatarctos." Because brown bears (Ursus arctos) and polar bears interbred in zoos, in 1953 Erdbrink & Thenius finally decided to choose "Ursus (Thalarctos) maritimus" as the scientific name of the polar bear. According to the fossil record, Kurtén in 1964 recommended the name "Ursus maritimus" named by Phipps in 1774, which was proposed by Harington (1966), Manning (1971) and Wilson (1976) and have been using it.

evolution

Polar bears are animals of the Ursidae family. Scientists have a consensus that polar bears evolved from brown bears. But the time of evolution is still controversial. Most previously believed that polar bears were the most modern bears, evolving about 150,000 years ago. Scientific research, including DNA, shows that polar bears have deviated from Ursidae based on information they obtained from polar bear remains from approximately 100,000 years ago. These are the oldest test remains ever found. Most researchers' theories about polar bear evolution are quite interesting. They believe that large numbers of brown bears were isolated from other populations during a period when parts of the world were covered in ice. Therefore, these brown bears evolved to adapt to the environment in which they survive. About 20,000 years ago, polar bears underwent one of the most dramatic changes. This has to do with the size and shape of their molars. They are very different compared to brown bear species. They enable them to move through ice, fight each other to mate, and kill prey quickly and easily.

In 2004, researchers discovered a polar bear fossil on a cliff off the coast of Norway. It is the lower left part of the jaw that still contains a tooth. Researchers used DNA sequences to infer sequences that the ancestors of polar and brown bears might have carried. After studying the fossil's anatomy, stratigraphy, and mitochondrial DNA (and the molecular clock in that DNA), the team looked at another piece of evidence unearthed with the fossil: the atoms that make up the teeth embedded in the jawbone. An organism's diet strongly affects the kinds of atoms that are deposited in its body - specifically the proportions of atoms with different numbers of neutrons. By studying carbon and nitrogen in the bears' teeth, the researchers found the ratios exactly what one would expect to observe bears getting nutrients from seafood. Just about 20,000 years after they separated from their forest-dwelling brown bears, polar bears have evolved their own unique marine lifestyle. For large mammals, this rate of evolution is extremely rapid.

One puzzling fact that experts ponder is that polar bears hibernate only partially. Pregnant females are due to give birth, but it is not a constant sleep state. It is believed that these bears evolved from the need to hibernate. They are able to survive by sucking nutrients from the layer of fat beneath their fur while awake. Other types of bears hibernate due to lack of food during certain times of the year. However, in most cases, this is not a problem for polar bears.

climate

This rapid evolution of polar bears may be related to climate changes at that time. Polar bear and brown bear lineages split during the Ice Age. This may have provided an ecological environment for the evolution of the seafood-eating, sea-ice-loving polar bear lifestyle. The newly formed polar bear lineage survived a warm interglacial period and then returned to another ice age. One of the main differences between the polar bear and other types of bears is its habitat. When this bear was first discovered, it was very strange that it would be living in such an extremely cold part of the world. There is evidence that more than 38 million years ago, an evolutionary process began that forever separated polar bears from other types of bears found around the world.

hybridization

Polar bears can hybridize with brown bears to produce fertile offspring, especially the brown bear subspecies in North America. Grizzly bears will hybridize with polar bears in the wild to produce the intermediate gray polar bear (Ursus maritimus × Ursus arctos). Genetic analysis shows that both Gene exchange still occurs from time to time, making the North American grizzly bear the brown bear subspecies closest to the polar bear, which also means that complete reproductive isolation between polar bears and brown bears has not yet been established.

Although the polar bear does fall into the category of bears, there is scientific evidence that it has evolved into a distinct species. This is because they differ in many ways from other forms of bears. The depth of this research continues because many elements of polar bears are still poorly understood. The brown bear is believed to be the species most closely related to it.

The fact that polar bears have evolved over millions of years is impressive. They are at the top of the food chain, which makes them a very important part of the Earth's world. When their numbers decline, the ecology is thrown out of balance. For example, there will be too many seals fighting for their food and natural habitat. The hope is that polar bears will have the extra evolutionary factors they need to survive for millions more years.

Some scientists also believe that the genetic diversity of polar bears in different regions is not large enough. Therefore, in the face of the crisis of climate change, polar bears lack genetic diversity, which may easily lead to their total extinction.

The body of the polar bear is large and sturdy, with a shoulder height of up to 1.6 meters. Adult males weigh between 300-800 kilograms and can reach 2.5 meters in length from the tip of their nose to the tip of their tail. Females are smaller, weighing 150-300 kilograms and 1.8-2 meters long. Similar to a brown bear, except without the shoulder hump. The head is relatively smaller than that of other bears, with small, round ears and a slender neck. The skin is black, and the original appearance of the skin can be seen from the black skin on the nose, paw pads, lips and around the eyes. The black skin helps absorb heat, which is a good way to keep warm. Polar bears have five toes on each foot and their claws cannot be retracted. The front paws are large and paddle-shaped, suitable for swimming and walking on thin ice. The hind legs are not used when swimming. The limbs and palms are hairy, and the soles of the hind and fore feet have fur for insulation and traction. Females have four functional breasts.

Polar bear fur is a colorless, transparent, hollow, small tube that lacks pigment and is usually white in appearance. The white appearance is the result of light refracting from the clear hair strands. However, in the summer it may appear yellowish due to oxidation, and may even appear brown or gray, depending on the season and light conditions.

Gear type: I 3/3, C 1/1, P 2 – /2 – 4, M 2/3.

Distributed in Canada (Labrador, Manitoba, Newfoundland, Northwest Territories, Nunavut, Ontario, Quebec and Yukon), Greenland, Norway, Russia (Yakutia, Krasnoyarsk , Western Siberia, Nordic Russia), Svalbard and Jan Mayen Islands, United States (Alaska). In addition, I occasionally wander to Iceland.

The southern part of the polar bear's range occurs in the northwest Atlantic Ocean off the coast of Newfoundland, Canada. The northernmost recorded observation of a polar bear is at 89°46'N, 25 kilometers from the North Pole. The southernmost known habitat is Akimiski Island in James Bay, Canada, approximately 52°35’N.

Habitat

The polar bear is an animal that can survive in harsh environments. Its active range is mainly in the sea areas with floating ice near the Arctic Ocean. The preferred habitat is the ice floes of the Arctic Ocean. Ice edges and pressure ridges where breakup and refreezing occur provide the best hunting grounds. As the ice melts and freezes, polar bears will travel up to 1,000 kilometers north and south. During the summer, they may remain on islands or coastlines with fixed ice, drift on ice currents or become trapped on land, where polar bears are forced to endure warmer weather.

Inhabits low mountain forest meadows. Live in areas with many caves. Winter burrows can reach depths reaching the permafrost. The nest chamber has plenty of grass to keep it warm. Before hibernation, a layer of silt is formed 25 cm above the overwintering chamber, and the outlet is sealed with soil and grass.

Circumpolar distribution of polar bears. They are found throughout the arctic regions around the North Pole. Their range limits are determined by ice in the Arctic Ocean and land ice in surrounding coastal areas. Polar bears have been reported as far south as Greenland and the southern tip of Iceland. During the winter, polar bears will move along the southern edge of the ice sheet or the northern edge of ice that forms along continental coasts. Pregnant females will overwinter along shorelines where habitat is available for the production of offspring. During the summer, polar bears will remain on the edges of receding ice or on islands and coastal areas where land ice remains.

Polar bears live in the ice-covered waters of the Arctic Circle. Although some occur in permanent multi-year ice floes in the central Arctic basins, they are most commonly found in annual ice on continental shelves and interisland archipelagos surrounding the polar basins. Polar bears with consistent access to sea ice can hunt year-round. However, in areas where sea ice melts completely each summer, polar bears are forced to spend several months on land, where they feed primarily on stored fat until the sea freezes. Land use by polar bears appears to be increasing during the ice-free season, at least in some areas where sea ice duration is decreasing.

senses

Polar bears, like other species of bears, have an extremely sensitive sense of smell and can detect scents within a radius of 1 kilometer or 1 meter under ice and snow. Use their sensitive lips and whiskers to explore objects. Their vision and hearing are not particularly developed. Polar bears purr as a greeting.

Activity

Polar bears are such excellent swimmers that they were once considered marine animals. Polar bears spend most of their lives (about 66.6%) in a "quiet" state, such as sleeping, lying down, or waiting for prey. The remaining 29.1% of the time is spent walking or swimming on land or ice. , 1.2% of the time is spent attacking prey, and the remaining time is basically enjoying delicious food. Sometimes the hard-caught prey of polar bears will attract the prying eyes of the same kind. Generally speaking, if unfortunately faced with those huge guys, smaller polar bears will be more inclined to run away. However, a mother who is nursing her young needs to protect her young. , or defend the family's hard-earned rations, and sometimes fight against the big male bears who come to offend.

hunt

Polar bears have two hunting strategies. Mainly used for still hunting. This involves finding a seal's breathing hole in the ice and then waiting for the seal to surface and kill it. When a polar bear sees a seal emerging from the water to bask in the sun, it will use tracking technology to get closer and then try to capture it. One tracking technique is to crouch and stay out of sight while catching seals climbing onto the ice. Another technique is to swim through any channels or cracks in the ice until it's close enough to capture the seal. Using this technique, polar bears can actually dive under the ice and into the water through their breathing holes in order to corral seals and cut off their escape routes. Predation usually occurs immediately after the prey is dragged out of the water. Polar bears eat the skin and fat first, and the rest is usually discarded. Other polar bears or arctic foxes then scavenge these leftovers. After eating, polar bears clean themselves by licking and rinsing their fur.

hibernate

Generally speaking, polar bears are very active from March to May every year, traveling around ice floes in search of food and living an amphibious life. In the severe winter, polar bears' outdoor activities are greatly reduced, and they can almost go without eating for a long time. At this time, they look for shelter from the wind and lie down on the ground to sleep. The respiratory rate decreases and enters partial hibernation.

The so-called partial hibernation, on the one hand, means that they are not hibernating like snakes and other animals, but they are sleeping but not sleeping. Once they encounter an emergency, they can wake up immediately to cope with changes. Plus, polar bears simply go without food or water for an extended period of time, not the entire winter.

Scientists have also suggested that polar bears may also have partial aestivation. That is, in the summer period when ice floes are at their lowest, polar bears may find it difficult to find food and may also be in a state of partial aestivation. One of the sources is that Canadian polar bear experts captured several polar bears with paws covered with long hair in the Hudson Bay in the fall. Experts speculate that they have little foraging activity in the summer otherwise the bear's paws would not be covered with long hairs.

feeding habits

Polar bears differ from other bears in that they do not store uneaten food to eat later. If whales are encountered, polar bears often eat only the blubber and discard the prey. The high caloric value of blubber compared to meat is important for polar bears to maintain an insulating layer of fat and store energy when food is scarce. They have a special way of eating, and their stomachs can hold 50-70 kilograms of food. It is the most carnivorous species among bears, with 98.5% of its food being meat. The main prey are ringed seals and, to a lesser extent, bearded seals. In some areas, they also prey on harp seals, hooded seals, and even larger species such as walruses and beluga whales. It also preys on seabirds, fish, and small mammals, and sometimes scavenges carrion. In summer they occasionally eat berries or plant roots. At the end of spring and summer, people will also go to the beach to pick up washed seaweed to replenish the minerals and vitamins needed by the body.

Polar bears are the top predators in the Arctic. The remains of seal prey that have not been eaten by polar bears may be an important food source for young, inexperienced polar bears and arctic foxes. Polar bears digest fat more efficiently than protein. Polar bears are large compared to other bear species, a result of their energy-rich diet. Polar bears are large compared to other bears, a result of their energy-rich diet. Although birds, fish, vegetation, and kelp are locally available during the ice-free season, polar bears are unlikely to obtain adequate nutrition if they survive on a land-based diet.

natural enemy

Humans and other polar bears are the polar bear’s only natural enemies and predators. Male polar bears may prey on polar bear cubs if other males approach them. For this reason, females with cubs tend to avoid other polar bears.

The polar bear was given its common name by Thomas Pennant in A Synopsis of Quadrupeds (1771). It was known as the "white bear" in Europe between the 13th and 18th centuries, as well as "ice bear", "sea bear" and "Greenland bear". The Norse referred to it as isbjørn ("ice bear") and hvitebjørn ("white bear"). The bear is called nanook by the Inuit. The Netsilik cultures additionally have different names for bears based on certain factors, such as sex and age: these include adult males (anguraq), single adult females (tattaq), gestating females (arnaluk), newborns (hagliaqtug), large adolescents (namiaq) and dormant bears (apitiliit). The scientific name Ursus maritimus is Latin for "sea bear".

Polar bears are a kind of "K selection" (R/K selection theory) with late sexual maturity, small litter size, high maternal investment, and high adult survival rate. Polar bears have the lowest reproductive rate of all mammals, although similar to other bears. Females typically mature at 4-5 years of age and enter a prolonged estrus period between late March and early June, although most mating occurs in April and early May. Ovulation is induced by mating, and implantation is delayed until autumn. The total gestation period is between 195-265 days. Whether the embryo implants and continues to develop is likely to depend on medical conditions. Pregnant females enter dens on land in snow or slopes, near the sea or sea ice (in the Chukchi and Beaufort Seas) as early as September-October, but more commonly in late autumn. The female gives birth inside the nest, usually in late December to early January. Polar bears most often give birth to twins per litter, with singles and triples being less common. The newborn polar bear cub is blind, has sparse hair, and weighs about 0.6 kilograms. They grow rapidly, feeding on their mother's rich milk (36% fat), and when they emerge from the nest sometime between early March and late April, they weigh 10-12 kg. In some areas, after emerging from the nest, females may go without food for up to eight months, possibly the longest period of food deprivation of any mammal.

Pup mortality is high during the first year, and the likelihood of pup survival depends largely on maternal condition. Mothers with greater fat stores in the fall have larger pups in the spring that are more likely to survive. Cubs typically stay with their mothers for two years, so females in most locations do not enter a new reproductive cycle more frequently than every three years, on average. In contrast to their low reproductive rates, adult polar bears have a high survival rate.

Polar bears have a continuous polygamous mating system. Male and female breeding pairs remain together for a short period of time. Mating occurs in late winter and early spring, from March to June. Delayed implantation extends the gestation period to 195-265 days. Pregnant females establish winter dens in October or November, usually in the snow within 8 kilometers of the coast. Between November and January, an average of two cubs are born in the mother's nest, with litter sizes ranging from 1 to 4. The mother bear remains in hibernation and cares for her cubs until April.

Pup mortality is estimated at 10-30%. A newborn polar bear is about 30 centimeters long and weighs 700 grams. The whole body is already covered with soft hair. It can walk when it is 1-2 months old. After 3-4 months, the mother bear leaves the cave with her cubs and lets them go out to see the world. , gain knowledge, and lead them back to the cave to spend the night at night; female polar bears will not leave the cave where they live when their babies are young. They will stay in the cave to convert the subcutaneous fat stored in their bodies to secrete milk to feed them. Provide your baby and yourself with the nutrients they need. Weaned 4-5 months after birth, the pups stay with their mother for 2-3 years. During this time, the cubs learn to hunt and survive in the harsh Arctic environment.

Both males and females reach sexual maturity at 5-6 years of age. In the wild, a polar bear's lifespan is estimated to be 25-30 years. Annual adult bear mortality is estimated at 8% to 16%. The oldest recorded lifespan in captivity was a female who died in 1991 at the Detroit Zoo in the United States at the age of 43 years and 10 months.

protection level

Listed in Appendix I, Appendix II and Appendix III of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Level I in 2019.

Listed in the "World Conservation Union Red List of Threatened Species" (IUCN) 2016 ver3.1 - Vulnerable (VU)

Population status

In 2010, the International Union for Conservation of Nature's Polar Bear Specialist Group (PBSG) recognized 19 subpopulation units of polar bears. Genetic studies show that there is gene flow between different subpopulations and there is no evidence that any units have been evolutionarily separated for a long time. Although individual exchange between subpopulations may be limited, some statistical and genetic exchange does occur. Therefore, polar bear subpopulations cannot be considered distinct population units and the term “management unit” may be more accurate. Continued reductions in the duration, distribution, and quality of sea ice due to climate change may lead to varying degrees of genetic and individual exchange between subpopulations in the future, which may result in new population dynamics or functionally isolated subpopulations.

In 2015, PBSG summarized the best scientific information on the status of 19 polar bear subpopulations in 2014, including an assessment of current trends (i.e., estimated changes in population size over a 12-year period, time-centered assessment). The PBSG concluded that 1 subpopulation (McClintock Strait) was increasing and 6 were stable (Davis Strait, Fox Basin, Busia Bay, Northern Beaufort Sea, Southern Hudson Bay, and Western Hudson Bay), 3 are thought to have declined (Baffin Bay, Kane Basin and Southern Beaufort Sea) and the remaining 9 (Arctic Basin, Barents Sea, Chukchi Sea, East Greenland, Kara Sea , Lancaster Sound, Laptev Sea, Norwegian Bight and Viscount Melville Strait) data provide an assessment of current trends. The type of data, precision, and time span used to estimate trends vary among subpopulations.

Estimating polar bear populations is expensive and difficult because the animals often occur at low densities in remote habitats. Although abundance estimates have generally improved in recent decades as of 2010, information on some subpopulations is still lacking or outdated. Aggregating the latest estimates for 19 subpopulations results in a total of approximately 26,000 polar bears (95% CI =22,000-31,000). Note that this number differs from the number obtained by summing abundance estimates in PBSG (2015) because the criteria for including abundance estimates in the two sources are different (abundance prediction section). The totals presented here do not include the Arctic Basin subpopulation, for which abundance information is not available. The 95% confidence intervals shown here were generated from simulations using uncertainty estimates and assuming that the abundance of each subpopulation is independent of the other subpopulations. The varying quality and lack of available information for each subpopulation means caution is needed when establishing and reporting a single estimate of polar bear numbers across the Arctic Circle. Therefore, abundance data are derived in a relative manner, scaling subpopulation-specific changes to global population-scale changes, rather than in an absolute manner.

Polar bears are not harmless to humans, but unrestricted hunting and killing will put polar bears at risk. The main threats facing polar bears include pollution, poaching and disturbance from industrial activities. While the effects of climate change are uncertain, it is recognized that even minor climate changes could have profound effects on polar bears' sea ice habitats. For example, if the Arctic icebergs continue to melt, polar bears may no longer be able to live in caves, which will affect the survival of polar bears and their cubs. If the roof and walls of the nest are not thick enough, the nest may collapse, killing seals and reducing the polar bear's food source. Persistent organic pollutants (POPs) also pose a threat to polar bears. Research on the accumulation of organochlorine pesticides shows that polar bears, as apex predators, are at risk of accumulating these compounds in their bodies, including in their nervous systems, reproductive and immune functions.

There are approximately more than 20,000 wild polar bears living in the world, and the number is relatively stable. In order to protect their survival, as early as 1972, the United States enacted a law prohibiting the hunting of polar bears except for survival needs. In 1973, countries in the Arctic Circle, including the United States, Canada, Norway, Denmark and the former Soviet Union, further signed an international convention to protect polar bears. In addition to restricting hunting and trade, the convention also further proposed the protection of their habitat and cooperation. Terms of Study.

On June 21, 2022, according to the China Science News, scientists discovered a new subspecies of polar bears near Greenland that does not require sea ice for hunting. Research believes that this subspecies may bring new hope for the survival of polar bears. Scientists published an article in Science that they discovered a group of unique polar bears in southeastern Greenland. These polar bears used a mixture of freshwater snow and ice as a platform to ambush seals. Researchers say this new population may offer hope for the bears' survival as Arctic sea ice shrinks due to global warming, putting many polar bears at risk of starvation.