Polar bear (scientific name:Ursus maritimus）: YesUrsidaeUrsusIs the largest land in the worldCarnivore, also known as white bear.The body is large and sturdy, and the shoulder height can reach 1.6 meters.Adult males weigh between 300-800kg and have a head length of 2.5m.The female is small, weighing 150-300kg and 1.8-2 meters long.Similar to the brown bear, but without shoulder hump.The head is smaller than that of other bears, the ears are small and round, and the neck is slender.The skin is black. Because the hair is transparent, it is usually white in appearance. It also has yellow and other colors. It is huge and fierce.Each foot has five toes. The claws cannot be retracted. The front claws are large and paddle shaped, suitable for swimming and walking on thin ice.
Polar bears live in the ice covered waters of the Arctic Circle.In winter, the depth of caves can reach permafrost.The preferred habitat is ice floes in the Arctic Ocean.The fractured and refrozen periglacial and pressure ridges provide the best hunting grounds.Generally acting alone, except during mating and lactation.About 66.6% of the time in a year is inactive, and 29.1% of the rest is spent on walking and swimming, tracking prey 1.2% or eating 2.3%.Polar bears are excellent swimmers, and they may find food in a wide range.It is the most carnivorous species, and 98.5% of the food is meat.The main prey is seals, and even larger species, such as walrus and beluga.They also prey on seabirds, fish, small mammals, and sometimes clean carrion.In summer, they occasionally eat berries or roots of plants.At the end of spring and the beginning of summer, you will also go to the seaside to take seaweed washed up to supplement the minerals and vitamins your body needs.
Polar bears are distributed in the ice covered waters of the entire Arctic Circle.In the area where the sea ice in the Arctic Circle completely melts every summer, polar bears are forced to spend several months on land, where they mainly feed on stored fat until the sea freezes.
In 1774, Phipps first described the polar bear as an independentspecies, and name it“Ursus maritimus”。It is recommended that other synonymous scientific names include“Thalassarctos”、“Thalarctos”And“Thalatarctos”。Because the brown bear（Ursus arctos）Hybridized with polar bears in the zoo. In 1953, Erdbrink and Thenius finally decided to choose“Ursus（Thalarctos）maritimus”It is the scientific name of polar bear.According to the fossil record, Kurt é n recommended the name of Phelps in 1774 in 1964“Ursus maritimus”The name was proposed by Harington (1966), Manning (1971) and Wilson (1976) and has been used all the time.[3]
evolution
The polar bear is a member of the genus Ursidae.Scientists have agreed that polar bears areBrown bearEvolved.But the time of evolution is still controversial.Most people believed that the polar bear was the most modern bear, which evolved about 150000 years ago.Scientific research, including DNA, shows that polar bears deviate from Ursidae based on the information they obtained from the remains of polar bears about 100000 years ago.These are the oldest test remains ever found.Most researchers' theories about polar bear evolution are very interesting.They believe that during the period when parts of the world were covered with ice, a large number of brown bears were isolated from other populations.Therefore, these brown bears evolved to adapt to the environment on which they live.About 20000 years ago, one of the most remarkable changes took place in polar bears.This is related to the size and shape of their molars.They are very different from the brown bear species.They enable them to cross the ice, fight each other for mating, and kill their prey quickly and easily.[4]
Polar bear fossils found in Norway in 2004
In 2004, researchers found a polar bear fossil on a cliff off the coast of Norway.It is the lower left part of the lower jaw and still has one tooth.The researchers used DNA sequences to infer the possible sequences carried by the ancestors of polar bears and brown bears.After studying the anatomical structure, stratigraphy and mitochondrial DNA (as well as the molecular clock in the DNA) of the fossil, the research team studied another evidence unearthed with the fossil: the atoms constituting the teeth embedded in the jaw bone.The diet of an organism will strongly affect the kind of atoms deposited in its body - especially the proportion of atoms with different neutron numbers.By studying the carbon and nitrogen in bear teeth, the researchers found that the proportion is exactly the proportion that people expect bears to get nutrition from seafood.Only about 20000 years after they separated from the brown bears living in the forest, the polar bears have evolved their own unique marine lifestyle.For large mammals, this rate of evolution is extremely fast.[5]
One puzzling fact that experts think about is that polar bears only hibernate locally.The pregnant female is due to give birth, but it is not a constant sleep state.It is believed that these bears evolved from the need for hibernation.They can survive in the sober state by absorbing nutrients from the fat layer under the fur.Other types of bears hibernate due to lack of food at certain times of the year.However, in most cases, this is not a problem for polar bears.[4]
climate
This rapid evolution of polar bears may be related to the climate change at that time.The lineage of polar bears and brown bears split during the Ice Age.This may provide an ecological environment for the evolution of the lifestyle of polar bears who eat seafood and like sea ice.The newly formed polar bear lineage survived a warm interglacial period and then returned to another ice age.One of the main differences between polar bears and other types of bears is their habitat.When this bear was first found, it was very strange that it would live in this extremely cold place in the world.There is evidence that more than 38 million years ago, evolution began to separate polar bears from other types of bears found around the world forever.[4-5]
hybridization
Polar bears can cross with brown bears to produce fertile offspring, especially the brown bear subspecies in North AmericaNorth American grizzly bearThey will cross with polar bears in the wildGrey polar bear（Ursus maritimus×Ursus arctos）Gene analysis shows that the two still have gene exchanges from time to time, making the North American grizzly bear the closest subspecies of brown bear to the polar bear, which also means that there is no complete reproductive isolation between the polar bear and the brown bear.[6]
Although polar bear does belong to the category of bear, there is scientific evidence that it has evolved into a clear species.This is because they are different from other forms of bears.Because many elements of polar bears are still unknown to people, the depth of this research is still continuing.It is believed that brown bears are the most closely related to them.[4]
The fact that polar bears have evolved over millions of years is impressive.They are infood chainThis makes them a very important part of the earth world.When their number drops, the ecology will lose balance.For example, there will be too manySealsFight for your food and natural habitat.It is hoped that polar bears will have the additional evolutionary factors they need to survive for millions of years.[4]
Some scientists also believe that the gene variability of polar bears in different regions is almost not large enough, so in the face of the crisis of climate change, polar bears lack diversity of genes, which is likely to lead to their overall extinction.[6]
morphological character
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Polar bears are large and strong, with shoulders up to 1.6 meters high.Adult males weigh between 300-800kg, and the length from nose tip to tail tip can reach 2.5 meters.The female is small, weighing 150-300kg and 1.8-2 meters long.Similar to the brown bear, but without shoulder hump.The head is smaller than that of other bears, the ears are small and round, and the neck is slender.The skin is black. The original appearance of the skin can be seen from the black skin around the nose, paw pad, lips and eyes of the polar bear. The black skin helps absorb heat, which is also 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.Do not use the hind legs when swimming.The palms are hairy, and the soles of the hind and forefoot have fur for insulation and traction.The female has four functional breasts.[7][10]
The polar bear's hair is a colorless and transparent hollow tube, lacking pigment, and is usually white in appearance. The white appearance is the result of light reflected from clear hair.However, in summer, it may be yellowish or even brown or gray due to oxidation, depending on the season and light conditions.[1][7]
Toothed type: I 3/3,C 1/1, P 2 – /2 – 4, M 2/3。[10]
Polar bear
Habitat environment
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Polar bear is an animal that can survive in harsh environment, and its range of activities is mainlyarctic oceanSea area with floating ice nearby.The preferred habitat is ice floes in the Arctic Ocean.The fractured and refrozen periglacial and pressure ridges provide the best hunting grounds.As the ice melts and freezes, polar bears will travel as much as 1000 kilometers north and south.In summer, they may stay on islands or coastlines with fixed ice layers, drift on ice streams or be trapped on land, and polar bears are forced to endure warm weather.[7]
It lives in low mountain forest and meadow.Living in a place with many caves.In winter, the depth of caves can reach permafrost.There is plenty of grass in the nest room to keep warm.Before hibernation, a layer of silt was formed 25 cm above the wintering room, and the outlet was closed by soil and grass.[3]
Polar bears are distributed circumpolar.They are all over the Arctic region around the Arctic.Their limits are determined by the ice in the Arctic Ocean and the land ice in the surrounding coastal areas.It is reported that there are polar bears as far south as Greenland and the southern tip of Iceland.In winter, polar bears will move along the southern edge of the ice sheet or the northern edge of the ice formed on the continental coast.Pregnant females will winterize on the shoreline where the habitat can be used to produce offspring.In summer, polar bears will stay at the edge of the retreating ice or in islands and coastal areas where land ice is preserved.[7]
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 basin, they are most commonly found on the annual ice on the continental shelf and the inter island islands around the polar basin.Polar bears that are in constant contact with sea ice can be hunted all year round.However, in areas where sea ice completely melts every summer, polar bears are forced to spend several months on land, where they mainly feed on stored fat until the sea freezes.Polar bear land use appears to be increasing during the ice free season, at least in some areas where sea ice duration is decreasing.[3]
Life habits
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sensory organs
Like other kinds of bears, polar bears have an extremely sensitive sense of smell, and can capture the smell of 1 km around or 1 m under snow and ice.Explore objects with their sensitive lips and whiskers.Their eyesight and hearing are not particularly developed.Polar bears use the sound of "grunting" as a greeting.[7]
activity
Polar bears are so excellent swimmers that they were once considered as marine animals.Polar bears spend most of their lives (about 66.6%) in a "static" state, such as sleeping, lying down for rest, 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 spent enjoying delicious food.Sometimes the prey that the polar bear catches hard will attract peers. Generally speaking, if it is unfortunate to face those big guys, the smaller polar bear will prefer to run away. However, a mother who is feeding a baby will sometimes compete with the big male bear who comes to offend in order to protect the baby or defend the family's hard won rations.[7][10]
Hunting
Polar bears have two hunting strategies.It mainly uses static hunting.This includes finding the seal's breathing hole in the ice and waiting for the seal to surface to kill.When a polar bear sees a seal coming out of the water to bask in the sun, it will use tracking technology to approach it, and then try to catch it.One tracking technique is to crouch and hide out of sight while capturing seals climbing on the ice.Another technique is to swim through any passage or crack in the ice until it is close enough to catch the seal.With this technique, polar bears can actually dive under the ice and on the water surface through their breathing holes in order to contain seals and cut off their escape routes.Predation is usually carried out immediately after the prey is pulled out of the water.Polar bears eat skin and fat first, and the rest is usually discarded.Other polar bears or arctic foxes then remove the leftovers.After eating, polar bears wash themselves by licking and rinsing their fur.[7]
dormancy
Generally speaking, polar bears are very active in March and May every year. They wander around the ice floe area to find food and live an amphibious life.In the severe winter, polar bears go out much less and can hardly eat for a long time. At this time, they seek shelter and sleep on the ground.The respiratory rate decreases and enters local hibernation.
The so-called partial hibernation, on the one hand, means that they are not hibernation of animals such as snakes, but sleep like sleep. Once encountering an emergency, they can wake up immediately to deal with emergencies.In addition, polar bears don't eat or drink for a long time, not all winter.
Scientists have also proposed that polar bears may also have partial hibernation, that is, during the period when ice floes are minimal in summer, polar bears may also be in partial hibernation when it is difficult to find food.One is that Canadian polar bear experts onceHudson BayCatch several polar bears with long hair on their paws.Experts speculate that they have little foraging activity in summer, otherwise the bear's paw will not be covered with long hair.[7]
Feeding habits
The difference between polar bears and other bears is that they will not store the leftover food and eat it later.If whales can be encountered, polar bears often only eat blubber and discard their prey.Compared with meat, the high calorific value of whale fat is important for polar bears to maintain an insulating fat layer and store energy when food is scarce.They have a special way of eating and a large amount of food. Their stomach can hold 50-70kg of food.It is the most carnivorous species among bears, and 98.5% of the food is meat.The main prey isringed seal , and those with smaller distribution rangeBearded seal。In some areas, they also preyHarp seal , crown seals, and even larger species, such aswalrusandbeluga。They also prey on seabirds, fish, small mammals, and sometimes clean carrion.In summer, they occasionally eat berries or roots of plants.At the end of spring and the beginning of summer, you will also go to the seaside to take seaweed washed up to supplement the minerals and vitamins your body needs.[7]
Polar bears are the top carnivores in the Arctic.The remains of seals not eaten by polar bears may be an important food source for young and inexperienced polar bears and arctic foxes.Polar bears digest fat more effectively than protein.Compared with other bear species, polar bears are very large, which is the result of their energy rich diet.Compared with other bears, polar bears are larger, which is the result of their energy rich diet.Although birds, fish, vegetation and kelp can be eaten locally in the ice free season, polar bears are unlikely to get enough nutrition if they live mainly on land.[3]
natural enemy
Human beings and other polar bears are the only natural enemies and predators of polar bears.If other males approach the polar bear cub, the male polar bear may prey on the cub.For this reason, females with cubs tend to avoid other polar bears.[7]
Distribution range
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It is distributed in Canada (Labrador, Manitoba, Newfoundland, Northwest China, Nunavut, Ontario, Quebec and Yukon), Greenland, Norway, Russia (Yakut, Krasnoyarsk, western Siberia, Nordic Russia), Svalbard and Jan Mayen Island, and the United States (Alaska).In addition, he occasionally wanders to Iceland.[3]
Polar bears occur in the southern part of their living area near the coast of Newfoundland, Canada, in the northwest Atlantic Ocean.The northernmost record of polar bears is 89 ° 46'N, 25 km away from the Arctic.The southernmost known habitat is located in theAkimiski Island, about 52 ° 35'N north latitude.[3]
Polar bear distribution map
Reproductive mode
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Polar bears are a kind of "K choice" with late sexual maturity, small litter size, high maternal investment and high adult survival rate“（R/K selection theory）。Polar bears have the lowest reproductive rate of all mammals, although similar to other bears.Females usually mature at the age of 4-5, and enter a long estrus period between late March and early June, although most mating occurs in April and early May.Ovulation is caused by mating, and implantation is delayed until autumn.The total gestation period is 195-265 days.Whether the embryo is implanted and continues to develop is likely to depend on the physical condition.Pregnant females enter the snow or slope on land, the dens near the sea or sea ice (in the Chukchi Sea and the Beaufort Sea) as early as September October, but more often in late autumn.The female gives birth in the nest, usually from late December to early January.Polar bears usually have twins in each litter, and there are fewer singletons and triplets.The newborn baby polar bear is blind, with sparse hair and weighs about 0.6kg.They grow rapidly and feed on their mother's rich milk (36% fat). When they come out of the nest at some time between the beginning of March and the end of April, their weight is 10-12 kg.In some areas, females may not eat for up to 8 months after coming out of the nest, which may be the longest food deprivation period of any mammal.[3]
The mortality rate of young is very high in the first year, and the possibility of survival of young depends to a large extent on the maternal condition.Mothers with larger fat stores in autumn have larger cubs in spring, and they are more likely to survive.Young bears usually stay with their mothers for two years, so females in most places do not enter the new reproductive cycle more frequently than every three years on average.In contrast to its low reproduction rate, adult polar bears have a high survival rate.[3]
Polar bears have a continuous polygamous mating system.Male and female reproductive pairs remain together for a short time.Mating occurs in late winter and early spring, from March to June.Delayed implantation will extend the pregnancy period to 195-265 days.Pregnant females usually establish winter nests in October or November in the snow within 8 kilometers of the coast.From November to January of the next year, on average, two cubs were born in the mother's nest, and the litter size ranged from one to four.The female bear has been hibernating and has been caring for her cubs until April.[7]
The infant mortality rate is estimated at 10-30%.The newly born polar bear is about 30cm long, weighs 700g, and is covered with soft hair;It can walk when it is 1-2 months old. After 3-4 months of birth, the female bear leaves the cave with her son, so that she can go out to see the world, learn more, and lead them back to the cave at night;Female polar bears will not leave the caves where their babies live when they are young. They will stay in the caves to convert the subcutaneous fat stored in their bodies to secrete milk to feed their babies and provide them with the nutrients they need.When weaned 4-5 months after birth, the cubs will live with their mothers for 2-3 years.During this time, the cubs will learn to hunt and survive in the harsh environment of the Arctic.[7]
Both males and females are sexually mature at the age of 5-6 years.In the wild, the life span of polar bears is estimated to be 25-30 years.The annual mortality rate of adult bears is estimated at 8% to 16%.In captivity, the longest living female recorded was a female who was in the United States in 1991Detroit Zoo He died at the age of 43 years and 10 months.[7]
In 2010, the Polar Bear Expert Group (PBSG) of the International Union for Conservation of Nature recognized 19 subspecies units of polar bears.Genetic research shows that there is gene flow between different subpopulations, and there is no evidence that any unit has been separated in evolution for a long time.Although individual communication between subpopulations may be limited, some quantitative statistics and gene exchange will still occur.Therefore, polar bear subpopulations cannot be considered as different quantitative units, and the term "management unit" may be more accurate.Due to climate change, the continuous reduction of the duration, distribution and quality of sea ice may lead to different degrees of genetic and individual exchanges between future subpopulations, which may lead to new population dynamics or functionally isolated subpopulations.[3]
In 2015, PBSG summarized the best scientific information about the status of the 19 subspecies of polar bears in 2014, including the assessment of the current trend (that is, to estimate the changes in population size during 12 years, time centered assessment).PBSG concluded that 1 subgroup (McClintock Strait) has increased, 6 are stable (Davis Strait, Fox Basin, Bucia Bay, North Beaufort Sea, South Hudson Bay and West Hudson Bay), and 3 are considered to have declined (Baffin Bay, Cairn Basin and South Beaufort Sea)The other nine (Arctic Basin, Barents Sea, Chukchi Sea, East Greenland, Karla Sea, Lancaster Strait, Laptev Sea, Norwegian Gulf and Viscount Melville Strait) data provide an assessment of the current trend.The data type, accuracy and time span used to estimate trends vary from subgroup to subgroup.[3]
Estimating the number of polar bears is expensive and difficult because these animals often appear in remote habitats at low densities.Although the estimates of abundance in recent decades have generally improved by 2010, information on some subpopulations is still lacking or outdated.A summary of the latest estimates for 19 subpopulations shows that there are about 26000 polar bears in total (95% CI=22000-31000).It is noted that this figure is different from the figure obtained by summing the abundance estimation in PBSG (2015), because the criteria for including abundance estimation in the two sources are different (quantity prediction part).The totals provided here do not include the Arctic Basin subspecies, whose abundance information is not available.The 95% confidence interval shown here is generated by simulation using uncertainty estimates, and it is assumed that the abundance of each subgroup is independent of other subgroups.The quality of each subspecies is uneven, even lacking of available information, which means that caution should be taken when establishing and reporting a single estimate of the number of polar bears in the entire Arctic Circle.Therefore, the abundance data is obtained in a relative way, scaling the changes specific to subgroups to the changes in global population size, rather than in an absolute way.[3]
Polar bears are not harmless to human beings, but unrestricted hunting and killing will threaten polar bears.The threats faced by polar bears mainly include pollution, poaching and interference from industrial activities.Although the impact of climate change is uncertain, it is recognized that even slight climate change may have a profound impact on the sea ice habitat of polar bears.For example, if the Arctic iceberg continues to melt, polar bears may no longer be able to live in caves, which will affect the survival of polar bears and their cubs.The top and walls of the nest are not thick enough, and the nest may collapse, killing seals and reducing the food source of polar bears.Persistent organic pollutants (POPs) also pose a threat to polar bears.Research on the accumulation of organochlorine pesticides shows that polar bears, as top predators, are at risk of accumulating these compounds, including nervous system, reproductive and immune functions.[3]
There are more than 20000 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 issued 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 on the protection of polar bears. In addition to restricting hunting and trade, the convention further proposed provisions for the protection of their habitats and cooperative research.[3]
On June 21, 2022, according to the report of China Science Daily, scientists found a new subspecies of polar bears near Greenland. Sea ice is not required for hunting. Research suggests that this subspecies may bring new hope for the survival of polar bears.Scientists reported in Science that they found a group of distinctive polar bears in the southeast of Greenland. These polar bears used a mixture of fresh water, snow and ice as a platform to ambush seals.Researchers said that with global warming and the reduction of Arctic sea ice, many polar bears are facing the threat of hunger, and this new population may bring hope for the survival of polar bears.[12]
Related culture
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The world's largest living land carnivore:The largest carnivore on land is the polar bear. Adult males usually weigh 400-600 kg, and the length from nose to tail is 2.4-2.6 meters.(Guinness World Records)
Bears living in the northernmost part of the earth:Polar bears live on the shrinking Arctic sea ice between 65 ° and 85 ° north latitude, but on August 5, 2001, an adult polar bear was found swimming at 89.775 ° north latitude.This place is about 24 kilometers away from the North Pole, which is the northernmost place where polar bears live ever recorded.(Guinness World Records)[2]
