Characteristics of populations:
Density: Polar bears’ home range can be very large. It depends on the habitat quality and the amount of food that is available. If polar bears live in food-rich areas they do not have to travel and have generally small home ranges, which can overlap with other bears. However, unlike most carnivores, polar bears are not territorial because they are constantly changing habitats due to the seasons changing. Scientists estimate that most polar bears limit travel to home ranges from 3-1000 miles. The consistent migration makes it difficult to pinpoint the exact population and density of polar bears. The density can be as high as 6 bears/100 square km or as low having have none. The average density is approximately 1 bear/100 square km. When on land the density can exceed 7 bears/100 square km. (Derocher, 2012)
Distribution: Polar bears may follow clumped or uniform distribution as they gather around food supplies but they (mother and cubs) must also compete against others for resources. Polar bears are nursed and taken care of by their mothers until they are approximately 2 and a half years old. They are then forced to become independent and will only interact with other polar bears during mating season. (Stirling, 2011)
Age structure: Not many bears make it past the age of 25. The oldest female was documented to be 32 years old and the oldest male was 28 years old (both found in James Bay, not including the bears in captivity). (Stirling, 2011)
Carrying Capacity: Polar bears are “K selected species”, population levels (in each region) are close to the carrying capacity. Females usually give birth to a few large young every 3 years and have decently high survival rates. Cub survival fluctuates between almost 100% to below 40% in other years, averaging to approximately 70% survival rate in the first year. Maternal investment is great and mortality rates decrease from birth to adulthood, creating a long lifespan. (Derocher, 2012)
Polar bear numbers in the Davis strait region have increased and the region may also have reached its carrying capacity. It is estimated that there is about 2158 bears in this area, and the density is approximately 5.1 bears/1,000 km2. (Derocher, 2012)
The irony in these studies are that because the Davis Strait area is experiencing a great loss of ice (due to global warming) it is indistinguishable whether the population is increasing and has reached its carrying capacity or if the area is decreasing, causing the same amount of bears to have a greater density. (Crockford, S.J. 2012)
Genetic Diversity: Although most sources will explain that due to a general decrease in population, there is also an decrease in genetic diversity. Through research conducted in Penn state University and Buffalo University, they have found polar bear genomes are beginning to resemble more like those of brown and black bears. They suggest that because of the warmer temperatures and the retreat of glaciers, polar bears and brown/black bears’ ranges overlap.This causes interbreeding, which increases genetic diversity. This could potentially provide polar bears with an advantage to surviving warmer temperatures. (Penn State University, 2012)