From earth.com:

Yellowstone National Park is a massive area of land spanning almost 3,500 square miles across the U.S. states of Wyoming, Montana, and Idaho. The park is home to crowd-pleasing animals such as bison, bears, and wolves – the latter of which were reintroduced to the park in the mid-1990s. After this reintroduction, some scientists believed that the wolves reestablished a “landscape of fear,” which resulted in elk – the wolf’s main prey – avoiding risky places where wolves hunted. This belief added to the burgeoning idea that predators affect prey populations and ecosystems through not only killing and eating prey, but by scaring them as well.

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