" In a paper evaluating the case for trophic cascades in the Annual Review of Ecology, Evolution, and Systematics, Peterson, Vucetich, and Douglas Smith, who trained on Isle Royale and now is a project leader for the Wolf Restoration Project at Yellowstone, argue that ecosystems are too complex to trace neat relationships, particularly in Yellowstone where grizzly bears, black bears, cougars, and wolves eat bison, deer, and elk. They also point out that, when you follow the threads of prey fluctuations, you often find at the source not wild-animal predators but human beings. "

― Sam Kean , The Best American Science and Nature Writing 2018