For over a century, wolves were persecuted in the United States and nearly became extinct. Gradually reintroduced, they are thriving again in the West, much to the benefit of the ecosystem.

"In 1995, the gray wolf was reintroduced to Yellowstone National Park after a seventy-year absence. All these years later, we can clearly see the cascading effects this has had on the park's ecosystem. This is a spectacular example of a trophic cascade, the term used when an important member of an ecosystem goes missing and many other living things are indirectly affected, causing a chain reaction of events. In the case of the reintroduced wolves...