Exploring a Specific Biogeographical Question: Polar Bears - Coursework Example

Polar bears Biogeography entails the study of both past and present distribution of different species in the world. It focuses on the assessment of the physical environment and its effects on species and their distribution on earth through studies of taxonomy and biomes. In this paper, biogeography will assist us in understanding of how evolution supports existence of polar bears, which are only found within the arctic area and not within the Antarctic region. Evolution of polar bears provided them with unique characteristics and features that enable it only survive in the arctic regions and not in any other part of the natural world. Thus, this is referred as endemism and provides answers to various questions concerning uneven distribution of species in the world. Introduction The polar bear is a carnivorous bear with a scientific name Ursus maritimus meaning the maritime bear. It is native to the Arctic Circle that encompasses the Arctic Ocean, the surrounding seas as well as surrounding landmasses. The polar bear is large with approximate same size as omnivorous Kodiak bear. An adult male polar bear (boar) approximately weighs from 350 – 700 kilogram while an adult female (sow) is half the weight of the male bear (Allen, 2013). The polar bear has evolved and currently occupies a narrow ecological niche despite being a sister species of the brown bear. Thus, through evolutionary divergence, the polar bear has adapted to cold temperatures, moving across snow, open water, and ice as well as adapting to hunting and consuming the seals, which constitute a large part of its diet (Allen, 2013). Fig 1: Bear in snow. The picture clearly demonstrates how animal is built for cold temperatures as well as beautiful adaption to the Arctic environment. Retrieved March 18, 2014 from http://www.polarbearsinternational.org/media/images/bear-snow The most striking observation is that many polar bears are born on land but spend much of their time living in sea thus the reason for its scientific name maritimus referring to maritime. Since seals comprise the preferred food for the polar bears, it hunts for it from the boundaries of sea ice. However, in case there is no sea ices, polar bear depend on its fat reserves for energy and this ensures its survival when there is no food (Bodden, 2010). Large-scale hunting of the polar bear that has occurred for decades led to its classification as vulnerable species since eight of its nineteen subpopulations were in decline. However, the raise of international alarm on the future of the polar bear led to rise in the populations due to the implementation of introduced quotas as well as controls. For a long time, the Arctic indigenous people have considered the polar bear as a prominent figure both in material, cultural and in their spiritual life and this continues in the present time. Body The evolution and taxonomy of polar bear According to scientific beliefs, the bear family known as Ursidae broke off from other carnivorans approximately 38 million years ago. Thereafter, the family Ursiane came into existence about 4.2 million years ago with the oldest known fossil of polar bear ranging between 130000 to 110000 years (Derocher & Wayne, 2012). This was a jawbone found in 2004 within Prince Charles Foreland. According to the fossil records, the molar teeth of the polar bear significantly changed from that of brown bear between 10000 to 20000 years back. Thus, the divergence of polar bears from a population of brown bears is believed to have occurred during the Pleistocene period when they became isolated. Thereafter, the ancestors of the polar bear underwent a sequence of evolutionary changes in order to survive within the harsh environmental conditions of the Arctic region (Derocher & Wayne, 2012). The new features and characteristics developed enabled it adapt to the life of preying on seals as well as surviving extreme cold temperatures. Consequently, the evidence from mitochondrial DNA analysis reveals that the divergence of polar bears from brown bears occurred around 150000 years ago. The mtDNA of the Irish brown bears is also close to that of polar bears thereby showing the existence of a relationship between the two species. Further, a comparison of the nuclear genome of the brown bears with that of the polar bears display a different pattern since the two constitute two discrete clades which diverged around 603000 years ago (Greenland & Laima, 1997). Moreover, the two animals have mated intermittently for a long time with most contact occurring during the warming periods. This was at a time when polar bears got pushed onto land while the brown bears migrate northward. Thus, these two types of animals mate and produce a fertile gizzly offspring hybrid of polar bear. Despite being genetically similar, both the polar bear and the brown bear cannot survive for a long time in another’s ecological niche due to different reasons ranging from differences in metabolism, morphology, phenotypic features and social as well as feeding behaviors (Greenland & Laima, 1997). Population and distribution of polar bears in the world The polar bear is found within the Arctic Circle as well as within the adjacent landmasses in then Newfoundland Island. The polar bear is rare in the north of 880 but its range traverses across the Arctic. Polar bear ranges include five countries namely Denmark (Greenland), the United States (Alaska), Russia, Norway (Svalbard) and Canada and who comprise the signatories to the International Agreement on the Conservation of Polar Bears. Fig 4. Polar Bear Population & Distribution Map. Retrieved March 18, from 2014 from http://www.polarbearsinternational.org/about-polar-bears/tracking/population-and-distribution The arctic is divided in four ice regions, which have 19 discrete subpopulations of polar bears whereby eight are on the decline, three remain stable, and seven have adequate data while one is on the increase. The four regions include the seasonal ice Eco region, Polar Bear Divergent Ice Eco region, Polar Basin Convergent Ice Eco Region and Archipelago Ice Eco region (Kallen, 1998). In the region, polar bears have to wait for ice to freeze during the fall to pave way for hunting since ice melts every summer. Polar bears within these seasonal areas are most endangered due to longer periods devoid of ice. In the Polar Bear Divergent Ice Eco Region, sea ice gets formed along the shoreline and thereafter later retreats more so during summer. As the sea continues to retreat inwards due to the warming of the Arctic, the polar bears have no choice but to come ashore and fast until the return of ice in the fall (Kallen, 1998). The polar bears in the region are therefore at a great risk of swimming long distances and fasting for long periods as well as encounter with human beings while searching food. The Polar Basin Convergent Ice Eco– Region consists of habitats with collections of ice along the shore and which provides the bears with access to food. Fig 3 Polar Bears & Sea Ice Regions. Retrieved March 18, from 2014 from http://www.polarbearsinternational.org/about-polar-bears/sea-ice However, scientists predict that unless there is a reduction in the production of CO2, then such areas will disappear in the next 75 years thereby posing a danger to the bears. The archipelago Ice Eco region consists of islands within the Canadian High Arctic as well as Greenland that are far away north and this enables them have sea ice throughout the year. This facilitates hunting among the polar bears. However, scientists predict the region as the last stronghold for polar bears but expected to melt in a 100 years’ time (OHare, 2008). The Seasonal Sea Ice Eco- occurs at the southern end of the ranges of polar bear such as Canada’s Hudson Bay. Due to lack of studies conducted on the ranges of the polar bear, it is hard to determine the exact population, but biologist approximates the number at around 20000 to 25000 in the entire world. Habitat/ ecological niche Polar bear is a marine mammal that lives mostly in the sea. Thus, it constitutes the only existing marine mammal possessing powerful, large limbs as well as feet enabling it to cover various miles on foot while also run on land (Patent & William, 2000). The preferred and favored habitat of the polar bear is the yearly sea ice enclosing the waters above the continental shelf as well as within Arctic inter- island archipelagos. This is because the annual ice consists of places where water appear as well as disappear all over the year in response to weather changes and thus seals which, constitute preferred meal for the polar bear do migrate in reaction to the changes. Thus, polar bears also move with the changing water patterns in search of prey (Patent & William, 2000). Physical characteristics The polar bear constitutes the biggest living creature of terrestrial predator with the adult male bear weighing around 350 to 700 kilogram and measure of 2.4 to 3 meters length. Consequently, the female weighs half the size of the males (Shores, 2006). It has a longer skull, nose, an elongated body with stocky legs and small ears and tail. The small and round ears as well as short tail helps in conserving heat in the extreme cold environment (Shores, 2006). Adaptations to the environment The reason why polar bears occur naturally in the Arctic region and within the sea ice is to increase accessibility to prey, which, majorly consists bearded, and ringed seals. They have evolved and adapted to the climatic conditions of the Arctic region (The National Geographic Society, 2014). After diverging from the brown bear in the Pleistocene period, the polar bear evolved separately in a new environment. The evolution has led to the development of certain features that enhance its survival within this extreme climatic region of the earth. The feet are large in order to distribute load when polar bear walk on thin ice and snow. Moreover, the large feet, which is 30 centimeters in length in an adult polar bear provides propulsion during swimming. Consequently, the black footpads at the underneath of the paws of polar bear are enclosed with small papillae, and this provides traction while moving on ice since they grip the ice and prevents the polar from slipping (Townsend & Gail, 2004). This ensures the animal perfectly roams in the Arctic environment. It also has short stocky, curved, strong, and sharp claws compared to those of the brown bear to assist in gripping heavy prey as well as provision of traction when on the ice. Further, it has deeply scooped claws on the underside, which assist in digging in the natural habitat as well as in the ice (Polar Bears International Organization, 2014). Consequently, what makes the polar bear survive in the Arctic environment is its ability to adapt to different levels of ice. For instance, when ice layers are thin, the animal extends its legs as well as lowering its body in order to assist in the distribution of its weight (Townsend & Gail, 2004). Moreover, the animal is an expert in placing each paw quietly and accurately when stalking seals. Moreover, the polar bear has forty-two teeth thus suggesting its carnivorous diet on seal. The cheek teeth are jagged and smaller as compared to those of the brown bear and this enables them shear off large pieces of meat from seals (The National Geographic Society, 2014). It also has large and sharp canines assisting in eating of the seals. Additionally, the development of long and widely spaced as well as sharp canines assists polar bear hold prey and thus enhancing its survival in the Arctic region where hunting of food is challenging The body of polar bear is superbly insulated up to 10 centimeters of blubber on their fur as well as hide, as this helps it overheat at temperatures exceeding 100C. Moreover, the fur consists of a dense insulating undercoat layer combined with an outer layer of guard hairs of varying lengths about 5 – 15 centimeters thick and extends in most parts of the body (Shores, 2006). These features insulate the polar bear from the cold and freezing environmental conditions within the Arctic region. Thus, polar bears remain warm and active throughout the year despite the presence of cold climate. The evolution of the thick fur coat on the polar bear prevents heat loss while it is on land or floating on sea ice. However, when in water, the animal depends on its fat layer to maintain warmth because wet fur is a poor insulator of heat. Since young cubs have little fat, mother cubs rarely swims with them in spring as they can become frozen. However, the dry fur of the cubs keeps them warm even at low spring temperatures such as -30 F (Shores, 2006). The animals also gradually moult from May – August but never shed their coat for the dark shade for purposes of camouflage during the summer weather conditions. During this period, the polar bear fasts since it cannot hunt for food due to the frozen nature of the sea at that time. However, this is possible since the animal depend on the fat reserves for generation of heat and energy for survival. Additionally, polar bear evolved a strong ability to detect and smell seals buried 1 meter under the snow and 1.6 kilometers away from it (Shores, 2006). This feature ensures the animal does not starve to death since it can easily locate its prey and consume it to gain energy for living. Therefore, the evolution and development of heightened senses in the polar bear enhances it survival chances within arctic conditions. The animal is a good swimmer and goes up to 300 kilometers from the shore of Arctic waters. This is made possible due to the buoyancy provided by the body fat. Moreover, while swimming, its forepaws serve as large paddles facilitating forward motion while hind paws act as rudders. The polar bear is capable of swimming at an approximate speed of 10 kilometer per hour. The neck of polar bear is very long, and this assists in swimming as well as when it thrust its head inside holes catching prey (OHare, 2008). Given that seals are endemic to the Arctic due to the favorable climate of changing waters, the polar bears because prefer eating the seal had to adapt to the Arctic environment. Thus, it hunts on the seals when they appear within holes in the ice to breathe or to rest. It commonly hunts the seals through still-hunting where it crouches and waits for the seal to appear and thereafter grabs it by use of forepaw. Other methods of hunting include stalking as well as through raiding of birth lairs of the female seals and grabbing them (Townsend & Gail, 2004). Apart from seals, the polar bear also consumes rodents, muskox, crustaceans, crabs, other polar bears, birds, and their eggs. Moreover, the polar bear consume garbage when they come closer to human beings. Such consumption pattern is dangerous since it can even lead to poisoning and even death. Behavior The polar bear is never territorial and often cautious during confrontations. Moreover, they never attack human beings unless when harshly provoked. However, hungry polar bears can harm human beings and even kill and eat people (Patent & William, 2000). They remain stealth hunters and often catch the victim unaware. Consequently, polar bears lead solitary lives but sometimes do play together. The polar bear is a threatened animal species due to natural and anthropogenic influenced activities. However, human activities contribute the highest threats to the existence of polar bears in the Arctic region. For instance, climate change occurring mostly from human activities has led to shrinkage in the extent and size of the Arctic sea from 1978 to 2002 (Kallen, 1998). Climate change occurs due to a buildup of greenhouse gases that cause global warming and leading to increased melting of Arctic sea ice. The fluctuation in levels of the sea ice makes it hard for the polar bears to find food as well as lead a normal life thereby causing stress, which eventually leads to death and extinction. This is because the polar bear depends on the sea ice to hunt, and thus removal, or reduction of the ice affects the ability of the animals to shrink. Fig 5. Scientists estimate that we could lose two-thirds of the worlds polar bears by the middle of the century unless we take action to reduce greenhouse gas emissions and stop climate change. Photo copyright Andrew Fore/Polar Bears International Polar Bears International Organization. Polar Bear Status Report. Retrieved March 18, 2014 from http://www.polarbearsinternational.org/science/polar-bear-status-report Consequently, man has significantly led to the pollution of the Arctic environment leading to the presence of toxic and harmful chemicals and substances in the ecosystem. In most instances, polar bears consume garbage from human wastes and this has often contributed to death and poor health of the polar bears (The National Geographic Society, 2014). Moreover, unsustainable harvesting and hunting of the polar bears by human beings threatens their existence and increases their chances of becoming extinct. There should be a better and wiser way of harvesting and hunting the polar bears in order to reduce chances of the species becoming extinct. Fig 2. Arctic climate temperature trend. Source: The Journal Science: University Corporation for Atmospheric Research. Retrieved March 18, 2014 from http://www.polarbearsinternational.org/about-polar-bears/tracking/sea-ice-loss Arctic Climate Temperature Pattern The loss and decrease of arctic sea ice corresponds with the increase in arctic temperatures, as depicted on the Fig 1 above. Over 2,000 years ago, Green indicates a steady cooling trend for the last 2,000 years. Blue illustrates decade-by-decade disparities. Red shows the sudden warming spike in current decades. In conclusion, I would recommend for the establishment of a proper and effective method of managing the polar bears since they are a unique cadre of animals being endangered as well as facing extinction. When such steps are considered and enforced, I am certain that the future generations would appreciate seeing this unique class of animals surviving in a specific extreme environment. References Allen, K. (2013). Polar Bears. North Mankato, Minn: Capstone Press. Bodden, V. (2010). Polar Bears. Mankato, Minn: Creative Education. Derocher, A. E., and Wayne L. (2012). Polar Bears: A Complete Guide to Their Biology and Behavior. Baltimore: Johns Hopkins University Press. Greenland, C., Laima, D. (1997). Polar Bears. New York: Scholastic. Kallen, S., A. (1998). Polar Bears. Edina, Minn: Abdo & Daughters. OHare, M. (2008). Do Polar Bears Get Lonely?: And 110 Other Questions. London: Profile. Patent, D. H., W., M. (2000). Polar Bears. nneapolis: Carolrhoda Books. Polar Bears International Organization. (2014). Paws, Claws, Ears and Tails. Retrieved March 18, 2014 from http://www.polarbearsinternational.org/about-polar- bears/essentials/paws- claws- ears-and-tails. Shores, E. L. (2006). Polar Bears. Mankato, Minn: Capstone Press. The National Geographic Society. (2014). Animals: Polar Bear. Retrieved March 18, 2014 from http://animals.nationalgeographic.com/animals/mammals/polar-bear/. Townsend, E., R, and Gail., Saunders-S. (2004). Polar Bears. Mankato, Minn: Pebble Books. Read More