What happens if you reintroduce wolves into the Yellowstone ecosystem? They hunt and kill deer. The deer population decreases. With the some of the deer gone, the levels of vegetation increase. Tall grasses and early successional plants replace plains. Trees grow taller. More and taller trees means bird and beaver populations increase. More beavers means more dams. As a result of the dams and the increase of trees by rivers, river banks collapse less often and became more fixed in their path. The increased trees and fixed rivers means that soil erosion sharply decreases, a boon to wildlife and the preservation of the ecosystem.
Reintroduce wolves, and you change the course of the rivers.
This is Ecology: the study of the interactions between all the biotic and abiotic forces that make up an ecosystem. It is a science of systems, of feedback loops, of unanticipated consequences. It is my favorite thing to study because the ecologist needs to think from the smallest level of algae in a lake to the largest level of erosion in the Grand Canyon. It is a fascinating science.
But more than that, it is a fascinating and universally applicable mindset. To be able to go from the smallest implementation detail to the largest overall goal, and to see how changes in one can ripple up or down to the other is not an easy thing to do, but it is what it takes to protect the planet.