An increase in the population of a species increases the chances of survival for that species. The species will be able to survive severe changes such as diseases and disasters. However, if the species moves into a new area, competition will increase for the species already in that area. The increased competition will negatively affect these other species.
They spend more time in their den, and they also put on "layers of fat" to have fat reserves to fall back on since they'll be less food in the winter :)
