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.
An estimated 20 to 30 million bison once dominated the North American landscape from the Appalachians to the Rockies, from the Gulf Coast to Alaska. Today, approximately 500,000 bison live across North America. However, most of these are not pure wild bison, but have been cross-bred with cattle in the past, and are semi-domesticated after being raised as livestock for many generations on ranches. Fewer than 30,000 wild bison are in conservation herds and fewer than 5,000 are unfenced and disease-free.