Prairie dogs are a keystone species. Over 150 other species depend on them as food, and, the habitat which they create. Five species of prairie dogs were once common across the central and western grasslands of North America, likely more than one billion strong. But the widespread destruction of prairie dog colonies and the arrival of diseases in the 1900s reduced prairie dogs by more than 95 percent. Today they exist in relatively small colonies scattered across 12 states in the U.S., one Mexican state, and one Canadian province.