This is conserving energy by going into a sleep-like state. This lowers the metabolism, allowing animals to extremely lower the amount of times they eat, drink, move, think, or defecate. When this occurs it allows them to survive lower temperatures by lowering their own. It also aids in winter, where there are no food or anything else for external energy sources. Hibernation is a means of lowering the amount of energy used to survive long-term harsh conditions.
A challenge between two organisms due to an overlap in their niche. They often fight till the death to get what they want. Other times it is to be the leader of the organism's pack. Organisms mark their territory to avoid this issue.