Historically, the American bison played an essential role in shaping the ecology of the Great Plains. They graze heavily on native grasses and disturb the soil with their hooves, allowing many plant and animal species to flourish. Prairie dogs prefer areas grazed by bison where the grass is short so they can keep a lookout for hungry predators, and wolves once relied on bison herds as a major food source. Today, wild bison are making a small comeback in a few scattered places, but they need more room to roam.