How bringing back lost species revives ecosystems

Few species evoke the spirit of the American wild as much as wolves

Scientists often study the grim impacts of losing wildlife to hunting, habitat destruction and climate change. But what happens when endangered animals are brought back from the brink?

Research has shown restoring so-called "keystone" species -- those with an outsized impact on their environment -- is vital for the health of ecosystems and can come with unexpected benefits for humans.

Here are some notable examples from North America. 

How bringing back lost species revives ecosystems