Wolves strike fear into the hearts of many species, humans included. Our fear of them has brought them to the edge of dying out, as we have cruelly killed them as competitors and trouble-makers. But researchers are discovering that the very fear they put into prey（被捕食者）species is exactly what helps make ecosystems（生态）healthy.
Yellowstone National Park is a typical example of just how wolves can help repair an ecosystem. An October 2018 study analyzed 40 years of research on large animals inside the park.
"Yellowstone has benefited from the reintroduction of wolves in ways that we did not anticipate, especially the complexity of biological interactions（互动） in the park," explained Mark Boyce, a professor in the Department of Biological Sciences." We were really surprised at that and we'd never have seen these responses if the park hadn't adopted ecological-process management—allowing natural ecological processes to take place with least human intervention."
After the wolves were re-introduced at Yellowstone, willow and cottonwood trees increased in number. The population of bears and bison also rose and what was once a ruling deer-wolf interaction is now more diverse.
To learn more about just how wolves are beneficial, a short documentary from Quest explains how the presence of wolves influences the behavior of deer, which eventually makes entire ecosystems more biologically diverse and healthy. In this documentary, biologist Aaron Wirsing explored why wolves and other top predators （捕食者）were needed for diverse ecosystems to develop. Using a simple video camera, Wirsing is gaining a unique view point on predator-prey relationships and changing the way we think about wolves.
The research is one more piece of evidence for why protecting these top predators is important not just for wolves as a species, but for hundreds of species at every level of an ecosystem. The fear they bring along may be the very angle that helps save them from dying out.
