How wolves change rivers > Task 1]]> One Question Per Page false false Wolves had never lived in Yellowstone National Park before 1995. 2 Before 1995, there were so many deer in the park that the ecosystem was suffering. 1 The main impact of the wolves was that they ate a lot of deer. 2 Plants in different parts of the park regenerated because the deer avoided them. 1 Wolves and beavers create specific habitats for other plants and animals. 1 The numbers of birds in the park also grew due to the increased availability of food. 1 The wolves made the rivers go in different directions. 2 This video shows that just one change can have a very big effect across a whole system. 1