By the 1920s, Yellowstone employees had exterminated all of the national park’s gray wolves, as directed by federal and state control programs. But in 1995, the wolves were reintroduced, and the apex predator has since reenergized the park’s ecosystems, producing positive effects that cascade down the food chain.
To avoid the preying wolves, the elk keep on the move, meaning they eat fewer of the young willow and aspen trees. With fewer elk eating young trees, that vegetation has since regenerated, creating habitats for beavers and songbirds. Elk carrion has provided food for scavengers like coyotes and eagles. And even river structure has improved, with the new, rich forests stabilizing the banks and reducing erosion.
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