What is a niche?
A niche is more than just the species' environment. A niche is made up of the species' habitat, place in the food web, how the species alters and is altered by its environment and other members of the ecosystem. A description of an animal's niche made include the temperature at which it can survive, the amount and type of food it consumes, the predators it has, whether it is active during the night or day, what competitors it has, and so forth.
According to the competitive exclusion principle, it is impossible for two species to occupy the same niche for an extended period of time.