This is an incredible video detailing the effects wolves have on the eco system! It first started by changing the behavior of the deer; they stopped going into certain areas they knew the wolves could catch them easily.
That enabled trees to grow higher than they ever have! They regenerated forests, stabilized the river banks which grew more vegetation which allowed for more wildlife to thrive.
The river changed in response to the wolves; they changed the physical geography by just existing within nature!
Source : thespiritscience.net