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I recently watched a video report on how the 1995 reintroduction of wolves to Yellowstone National Park—after a 70-year absence—altered the park’s entire ecosystem. Yes, wolves are predators, but as the video explains, “they give life to many others.”  Without wolves, the deer population exploded, with the animals grazing away much natural vegetation and reducing the park’s animal and plant diversity. As soon as the first wolves showed up, things started changing, They, of course, killed some deer. But they also changed the behavior of the deer, and that led to a “trophic cascade” which caused an explosion in the number and variety of plants and animals — and that changed the nature of the rivers. “So the wolves, small in number, not only transformed the ecosystem of Yellowstone National Park, but also its physical geography.” At AEI Ideas