Characteristics of population |
-Primary Characterisitcs |
Primary characterisitics As of 2014, there is an estimated 20000-25000 polar bears alive on the planet. Polar Bears inhabit most arctic regions, 60% of which are estimated to be in Canada. Their populations are commonly divided into 19 subpopulations, 13 of which are located in Canada. Though sufficient data cannot be provided for some areas the polar bear lives, it can be estimated as to how many polar bears are currently living in each area("Polar Bear Fact Sheet," n.d.). Polar bear populations are monitored through census studies, satellite tracking, aerial surveillance and population projects. These methods allow for scientists to track migration, hunting and home range patterns as well as monitor population health and numbers.
Figure 2: The 19 subpopulations are stated above, along with estimated population size and the current status and trend in population.
Polar Bears are territorial and do not travel in packs, but rather will live alone, except when the mothers raise their young. Polar bears have large home ranges and travel due to seasonal changes and the movement of seals("Home Range and Cold," 2014). Polar Bears have large home ranges due to these factors that can be as large as 1000km2 and will often cross over with other polar bears. Polar bears exhibit both uniform and clumped formation. The clumped formations can be seen in the 19 subpopulations of polar bears. Within these areas, depending on the resources the polar bears will be uniformly distributed. As seen in Figure 2 each sub population has varying population size, status and trends(Vongraven & Richardson, 2011). Areas such as Southern Beaufort Sea have been experiencing a decline in population due to ice loss and increasing human interference (the arctic has many large oil reserves) which causes for not enough resources for all of the population. Other areas such as the M'Ckiuntock Channel have been experiencing an increase in growth, due to a smaller subpopulation allowing for an abundance of resources(Evans, 2012).
Genetic Diversity Polar Bears are estimated to have split of from grizzly bears about 4000000-500000 years ago due to an increase in genetic diversity allowing for the bears to be able to endure colder environments. Today the genetic diversity of polar bears has become increasingly lower. Due to an overall small population size, approximately 25000 bears, that then breaks of into groups with populations lower than 100 bears. The genetic diversity of polar bears has gone through many bottleneck periods, due to climatic changes that favored certain individuals(Wilson, 2014). This has lead to increasingly less diverse genetics. The low genetic diversity of polar bears is worrisome because it would imply that changes in the ecosystem may not be handled well. Fewer individuals have the ability to survive changes, meaning that many individuals may be wiped out if a factor in the ecosystem where to change. The low genetic diversity causes for uncertainty in the numbers for polar bear populations in the upcoming years. The low diversity does not appear to have much of an effect on the species, but with the warming weather some of the bears will not have the ability to adapt.
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Figure 1: The above picture exhibits population size and distribution according to the geographical area("Polar Bear Status, Distribution," n.d.)
The population density of polar bears varies throughout each subpopulation. Each subpopulation ranges in size and population. Some areas, like the Gulf of Boothia, are estimated to have 18.3 bears/1000km2 while other areas have estimated densities at 1.4 bears/ 1000km2(Crockford, 2013). The population density varies on where there are more resources. Polar bears depend heavily on sea ice to survive. This is where they spend most of their lives. It is their hunting (mainly sea life like sea lions), mating and child raising area. Figure 3: The above figure exhibits the population density in the 13 areas that exist in Canada(Crockford, 2013).
life history of polar bears The life history of a species describes the patterns exhibited due to life span and reproductivity. It can be described through r-selected and K-selected strategies.Polar Bears have a K-selected strategy. This means that they have few offspring, a high level of parental care, long life spans and mature sexually later in life. Female Polar bears are the sole caregivers to baby cubs. A female polar bear will generally have 2-4 cubs (rarely over 2 cubs). Polar bears are primarily solitary animals, but a mother bear will take care of her cubs for up to 3 years after birth. In this time she teaches the cubs migration patterns, how to catch seals and any other life skills needed for the cubs to mature(Durner & Amstrup, 2005, p. [Page 2]). Female polar bears can produce up to 5 litters in their lifetimes. Since the mothers take up a lot of time raising 2-3 cubs, they have a low level of fecundity, but a higher level of survivorship due to the high level of maternal care. Polar Bears like most mammals therefore exhibit type 1 survivorship as shown in figure 4. Polar bears have long lifespans and typically live through childhood.
Figure 4: The following figure shows different types of survivorship. Type I- Many offsping, few live to their estimated average life span. Type II- Population is a mix of both other types, has an medium size of offspring born and able to survive for their average life span. Type III- Low amount of offspring, most live to their average life span.
carrying capacity Polar bears are described as K-selected organisms. K-selected organisms often live close to their carrying capacity, because they are able to maintain population levels due to the high level of parental care. In an area with a high abundance density dependent factors and little interference from humans (either through hunting or destruction of habitats/ecosystem), this can be seen. For example in figure 2, the four stable subpopulations are examples where carrying capacity is reached. These areas have an abundance of land, ice water and seals all needed for the survival of polar bears. This number will not increase due to the fact that there are not enough resources to sustain more individuals and it will not decrease unless on of the life dependent factors are changed (Evans, 2012). The carrying capacity in the one subpopulation that has shown to be increasing in population exhibits an area where there are more resources than the current population needs. The subpopulations that show a decrease in population suggests that there are not enough resources to uphold the current population. This is most likely due to climate change; not enough ice available for polar bears to hunt mate and raise children.
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Polar Bears have gone through many periods of struggle where there numbers have been low. The bottle neck effect has reoccurred many times in the past, a small population funding the next generation. Due to the K-selected strategy polar bears have often come out on top, and have been able to successfully rebuild their population numbers. Polar bears are one of the greatest success stories in conservation, seeing as how their numbers have grown since 2008, when they were placed under "threatened." Though polar bears are seen as a population that does fluctuate, the fluctuations it has been experiencing in the last few years has been primarily due to climate changes/human interaction and not other factors such as genetic diversity.
References
Crockford. (2013, August 29). POLAR BEAR POPULATION DENSITY [Blog post]. Retrieved from Polar Bear Science website: http://polarbearscience.com/tag/polar-bear-population-density/
Durner, G., & Amstrup, S. (2005). Polar Bear Maternal Den Habitat in the Arctic National Wildlife Refuge, Alaska. In Arctic (Vol. 59, pp. 1-6). Retrieved from Arctic database.
Home Range and Cold Climate. (2014). Retrieved November 23, 2014, from Polar Bears International website: http://www.polarbearsinternational.org/about-polar-bears/essentials/home-range-and-cold-climate
Evans. (2013) Marine Mammals. In K. M. Evans, Information Plus Reference Series. Endangered Species (2012 ed.). Detroit: Gale. Retrieved from http://ic.galegroup.com.ezproxy.torontopubliclibrary.ca/ic/ovic/ReferenceDetailsPage/ReferenceDetailsWindow?failOver&query=&prodId=OVIC&windowstate=normal&contentModules=&display-query=&mode=view&displayGroupName=Reference&limiter=&currPage=&disableHighlighting=false&displayGroups=&sortBy=&search_within_results=&p=OVIC&action=e&catId=&activity&scanId
Polar bear fact sheet. (n.d.). Retrieved November 23, 2014, from World Wildlife Foundation website: http://www.wwf.ca/conservation/species/polar_bear_factsheet.cfm
Polar bear status, distribution & population. (n.d.). Retrieved November 23, 2014, from World Wildlife Foundation website: http://wwf.panda.org/what_we_do/where_we_work/arctic/wildlife/polar_bear/population/
Vongraven, D., & Richardson, E. (2011, November 8). Biodiversity - status and trends of polar bears. Retrieved November 23, 2014, from Arctic Report Card website: http://www.arctic.noaa.gov/report11/biodiv_polar_bears.html
Wilson, A. (2014). Polar Bear DNA. Retrieved November 23, 2014, from California Academy of Sciences website: http://www.calacademy.org/explore-science/polar-bear-dna
Crockford. (2013, August 29). POLAR BEAR POPULATION DENSITY [Blog post]. Retrieved from Polar Bear Science website: http://polarbearscience.com/tag/polar-bear-population-density/
Durner, G., & Amstrup, S. (2005). Polar Bear Maternal Den Habitat in the Arctic National Wildlife Refuge, Alaska. In Arctic (Vol. 59, pp. 1-6). Retrieved from Arctic database.
Home Range and Cold Climate. (2014). Retrieved November 23, 2014, from Polar Bears International website: http://www.polarbearsinternational.org/about-polar-bears/essentials/home-range-and-cold-climate
Evans. (2013) Marine Mammals. In K. M. Evans, Information Plus Reference Series. Endangered Species (2012 ed.). Detroit: Gale. Retrieved from http://ic.galegroup.com.ezproxy.torontopubliclibrary.ca/ic/ovic/ReferenceDetailsPage/ReferenceDetailsWindow?failOver&query=&prodId=OVIC&windowstate=normal&contentModules=&display-query=&mode=view&displayGroupName=Reference&limiter=&currPage=&disableHighlighting=false&displayGroups=&sortBy=&search_within_results=&p=OVIC&action=e&catId=&activity&scanId
Polar bear fact sheet. (n.d.). Retrieved November 23, 2014, from World Wildlife Foundation website: http://www.wwf.ca/conservation/species/polar_bear_factsheet.cfm
Polar bear status, distribution & population. (n.d.). Retrieved November 23, 2014, from World Wildlife Foundation website: http://wwf.panda.org/what_we_do/where_we_work/arctic/wildlife/polar_bear/population/
Vongraven, D., & Richardson, E. (2011, November 8). Biodiversity - status and trends of polar bears. Retrieved November 23, 2014, from Arctic Report Card website: http://www.arctic.noaa.gov/report11/biodiv_polar_bears.html
Wilson, A. (2014). Polar Bear DNA. Retrieved November 23, 2014, from California Academy of Sciences website: http://www.calacademy.org/explore-science/polar-bear-dna