The population of Polar Bears continues to grow until the ice caps started melting so there was less space available, so the rate of reproduction of Polar Bears stopped. Also the land is an affect of the rate of Polar Bears decreasing because there isn't a lot of land, which makes competition harder. The reason why the data levels out it due to the fact that they have reached a carrying capacity because their isn't enough resources for the whole population of Polar Bears.
Due to global warming the ice caps have been melting which is a density-independent limiting factor. On the other hand, because the ice caps are melting competition between the species in the Artic Region has increased, this is known as density-dependent limiting factor. Competition between certain organisms would be for shelter, food, and could affect their niche.
Due to the melting ice caps Polar Bears are forced to immigrate out of the area, which leaves more carrying capacity for other Polar Bears. This benefits the other Polar Bears that decide to stay in the Artic Region, because it leaves more space to live and allows them to have less competition and survive. However, when Polar Bears emigrate into the population the resources become even more limited making it harder for them to survive.
Birth rates of Polar Bears have decreased due to the ice caps melting because the mothers often have miscarriages due to limited resources causing the cubs to be unhealthy and die. Since, the birth rate has decreased over the years the availability of resources has increased. The resources have increased because there aren't that many Polar Bears in the population fighting for the same resources.
Death Rates of Polar Bears
According to this data, from the points of 15000 to 30000 the Polar Bears population is increasing due to them not reaching a carrying capacity. From then on their population growth decreases because they started reproducing and eventually had too many organisms reproducing that it made it harder for them to survive.
Another reason for density-independent limiting factor is humans hunting Polar Bears. The population is dying due to the humans coming into their population and killing them.
Another example of density-dependent limiting factors is competition for resources, if the population has reached a carrying capacity it will be harder to find food(like fish).