Yellowstone National Park is a huge nature reserve. In general, humans beings don't intervene in the regulation of the ecological system of this reserve. However, in 1995, they have reintroduces the gray wolves. It was a necessary decision due to the increase of the elk population. Originally, gray wolves were settled in this area, but they were killed by farmers. Nowadays, gray wolves are protected by a law. The reintroduction of this animal is a success but there is a lot of another big predatory in Yellowstone. Among these predatory, the more famous is the grizzly. Both eat the same preys and during winter it's a very considerable fight between wolves and grizzlies to find food. We can note that they target each other's young as prey.