Rescuing Wildlife - Yellowstone National Park (U.S. National Park Service) On This Page Navigation. Yellowstone preserves one of the largest, temperate-zone ecosystems on Earth. About 99% of the park is managed as wilderness and our focus is on sustaining viable populations of native wildlife species, rather than protecting individual animals. Animals roam freely on a landscape not dominated by humans. An animal’s survival depends on its own daily decisions and natural selection. Animals with traits that make them better adapted to the environment will tend to survive, reproduce, and pass on their genetic characteristics more than animals without those traits. Through this process, natural selection shapes the behavior of wildlife. The death of some animals is a necessary part of sustaining our populations of predators, scavengers, decomposers and, eventually, herbivores once the nutrient cycle comes full circle.