When wolves were reintroduced to Yellowstone National Park in the United States in the mid-1990s, after being absent nearly 70 years, the most remarkable trophic cascade occurred, effecting hundreds of other species.
If you have not seen this video please do, www.youtube.com/watch?v=ysa5OBhXz-Q
Trophic cascades occur when predators in a food web suppress the abundance or alter traits (e.g., behavior) of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore).
For example, if the abundance of large piscivorous fish is increased in a lake, the abundance of their prey, zooplanktivorous fish, should decrease, large zooplankton abundance should increase, and phytoplankton biomass should decrease. This theory has stimulated new research in many areas of ecology.
Trophic cascades may also be important for understanding the effects of removing top predators from food webs, as humans have done in many places through hunting and fishing activities.
Photos are from Yellowstone National Park, Wyoming, USA, that I visited a few times this summer when working for The Nature Conservancy, J Bar L Ranch, Two Dot Land & Livestock and Yellowstone Grassfed Beef.
In the photos you see a buffalo, a black bear and two wolves eating on a dead buffalo.