This is a fantastic video that tells an amazing story about how the reintroduction of wolves into Yellowstone park made a huge difference to the local ecology, turning it from a place on the edge of collapse back into a thriving ecosystem:
It's really nicely told, ties things together into a neat story, and is well worth a watch.
Sadly, it's also a massive over-exaggeration, taking snippets of truth and weaving a mythology around them whereby a few awesome looking predators can reverse decades of mismanagement and Make Everything OK*.
I swear my gravestone is going to have "It was more complicated than that" written on it.
*Details