What do bison, beaver, wolves and sea otters all have in common?
They're keystone species. That means they have an outsized impact on their ecosystem. It took humans driving some of these to near extinction to realize just how important they are.
Now animals like the American Bison and North American Beaver are some of the Endangered Species Act's most notable success stories.
As part of our series marking the 50th anniversary of the Endangered Species Act, we're taking a closer look at the efforts to save keystone species.