Wolves were reintroduced into Yellowstone Park in 1995. Prior to this time, they were a major predator in the park. Their reintroduction after a decade resulted in a change in the behavior of the Elk which now had a large population in the park and appeared in large herds.
The Elk's behavior has also changed as they do not move into farther thickets so as not to be attacked by wolves. Also, they no longer move to open fields where they grazed as herds to avoid being preyed upon by lions. Vegetation is now restored due to this change in behavior of the Elk.
