After wolves were exterminated in Yellowstone National Park in the early 1900s, a domino of effects from their loss led to an almost complete collapse of the wetlands ecosystem. Now the wolves are back—after 66 were introduced between 1995-1996, the population has reached 200 packs with 1,700 members—and so are the wetlands.
So what happened? As the Los Angeles Times explains, removing the wolves created a chain of events that led to the land basically drying up. (Elk thrived and ate up willow seedlings, which beavers needed to create dams, and on and on). "The reintroduction has succeeded in ways that extend far beyond the health of the wolves themselves," writes Chip Ward. "It has reshaped an entire ecosystem."