How Wolves Change Rivers  

I quite liked this video on the impact of re-introducing wolves in Yellowstone national park - How Wolves Change Rivers.

The narration is taken from this talk by George Monbiot at TEDGlobal in 2013 - George Monbiot: For more wonder, rewild the world.

Wolves were once native to the US' Yellowstone National Park — until hunting wiped them out. But when, in 1995, the wolves began to come back (thanks to an aggressive management program), something interesting happened: the rest of the park began to find a new, more healthful balance. In a bold thought experiment, George Monbiot imagines a wilder world in which humans work to restore the complex, lost natural food chains that once surrounded us.