Exterminating wolves from Yellowstone de-watered the land. Their reintroduction has brought it back and more. Courts and government agencies are still sorting out how the wolves should be managed — scientists and tourists are delighted and ranchers dismayed — but it's clear the reintroduction has succeeded far beyond the health of the wolves themselves. "The unexpected relationship between absent wolves and absent water is just one example of how large predators such as grizzlies, wolves and mountain lions regulate their ecosystems from the top down. The results are especially relevant in an era of historic droughts and global warming."