https://www.theguardian.com/science/grrlscientist/2014/mar/03/how-wolves-change-rivers Wolves are crucial for maintaining a healthy ecosystem -- a fact that was conveniently forgotten when they were exterminated from almost all of the continental United States by ranchers, farmers, trappers and hunters. Meanwhile, the populations of other animals exploded. The entire ecosystem of the American wilderness was changed by rapidly expanding populations of large ungulates. After decades of political wrangling with those who traditionally persecuted wolves, conservation biologists and activists who supported restoration of wolves finally prevailed: the grey wolf, Canis lupus, was finally reintroduced several areas in the northern Rocky Mountains of the United States. One of those release areas was Yellowstone National Park. Subadult wolves from several packs in Alberta's Mackenzie Valley were captured using tranquilizer darts and released in Yellowstone in January 1995 and again in January 1996. Credit: The Guardian, GrrlScientist - an evolutionary biologist and ornithologist who writes about evolution, ethology and ecology, especially in birds.