Species Interactions - Polar Bears

Interactions

Polar bears are solitary animals. They live a life with minimal interaction with their own species other than when they mate or when the females raise their children. Polar bears are at the top of the food chain and are therefore are the predators of the north. Even humans have difficulty hunting the massive animals(Year, n.d.). Polar bears interact with little other animals, other than to prey upon them. The main and most popular interaction the polar bear experiences is that with seals. Polar bears also interact with the famous killer whales. A third species killer whales interact with are walruses.

Seals

There are many organisms that the polar bear eats, but their primary source of food are seals. This type of interaction is better known as predation. Seals are found throughout the arctic, the most common being the ringed seal. They are an important part in the polar bears diet seeing as how they are a major source of fat ("Polar Bear Diet," n.d.). One way polar bears hunt seals is through stalking. 
Ringed seals create hoes in ice to use as breathing holes. Since most of the animals that hunt seals are mammals, most of them need oxygen and therefore cannot go under this sea ice, because they might suffocate. This allows for the seals to be safe as long as they stay near their breathing holes and under the ice. Polar bears will find these holes and wait for the seals to come. This is when  they will kill and eat the seal ("Hunting and Diet," 2014).
Figure 1: Pink- seal population Blue-polar bear population

killer whales

Killer whales also known as Orcas are probably one of the most popular aquatic creature. The killer whale like the polar bear is at the top of the food chain and eats different types of marine life. The relationship the killer whale and polar bear share is competition. Killer whales like polar bears also live in the arctic and therefore share some of the same food choices as the polar bear, particularly in seals(Smith, n.d.). Polar bears also are known to eat dead Orcas if they happen to wash up on shore, which would make the polar bear a scavenger in this case. The polar bear population is not effected by this competition greatly, mainly because prey in the arctic are ample. There are estimated to be over 7 million seals in the Canadian arctic, which is more than enough for the 25000 polar bears and Orcas to share.
 Since seals are the primary source of food for polar bears, they are an important factor in population growth and size. Predation follows a sinusoidal and cosine graphs. One population grows while the other falls. It is a cycle that carries on each year. If there are lots of polar bears more seals will be eaten, the next year there will not be enough seals for polar bears to survive(Brookes, 2013, p. [Page 525]). The loss of polar bears will then cause for more seals to survive and the cycle continues as seen in figure 1. This relationship is not as impactful as a whole due to the amount of seals in comparison to the amount of bears, but in smaller regions the shifts in population can be seen.

Walruses

Walruses like seals and polar bears are arctic mammals. They are large and able to protect themselves so it is a surprise that the polar bear would to be able to overpower one. Most walruses travel in groups so when a polar bear does attack a walrus, he is usually not alone. A herd of walruses will not scare away a polar bear rather these bears will look for a more vulnerable individual (young or asleep), and attack it (Wildlife Arkive, 2011). Like the seals there are many more of the walruses versus the polar bears and they are not targeted nearly as much so the population size of polar bears is not effected by the population of walruses.
Refrences
Brookes, L. (Ed.). (2013). Biology 12.

Hunting and diet. (2014). Retrieved November 23, 2014, from Polar Bears International website: http://www.polarbearsinternational.org/about-polar-bears/essentials/hunting-and-eating

Polar bear diet. (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/diet/

Smith, T., Dr. (n.d.). Killer Whales "Gang Up" to Capture Seal. National Geographic. Retrieved from http://video.nationalgeographic.com/video/orca-juvenile-training-lex

Wildlife Arkive. (2011, January 24). Retrieved from http://www.arkive.org/walrus/odobenus-rosmarus/video-11.html

IUCN Red List (June, 2009) http://www.iucnredlist.org/, Kastelein, R. (2008) Walrus. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.,CITES (June, 2009) http://www.cites.org/, Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO Species Identification Guide. Marine Mammals of the World. Food and Agriculture Organization of the United Nations, Rome., Burnie, D. (2001) Animal. Dorling Kindersley, London., Kastelein, R.A. (January, 2011) Pers. comm., Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford, Nowak, R.M. (1999) Walker's Mammals of the World. Johns Hopkins University Press, Baltimore,Center for Biological Diversity (October, 2009) http://www.biologicaldiversity.org/news/press_releases/2009/pacific-walrus-09-08-2009.html, Taylor, M.F.J., Suckling, K.F. and Rachlinski, J.J. (2005) The effectiveness of the endangered species act: a quantitative analysis. Bioscience, 55(4): 360-367, Clark, J.A., Hoekstra, J.M., Boersma, P.D. and Kareiva, P. (2002) Improving U.S. Endangered Species Act recovery plans: key findings and recommendations of the SCB Recovery Plan Project. Conservation Biology, 16: 1510-1519.

Year, J. (n.d.). Polar Bear. National Geographic. Retrieved from http://animals.nationalgeographic.com/animals/mammals/polar-bear/