In the 1940s, 50 North American beavers (Castor canadensis) were introduced to the area by the Argentine government to help start a fur industry — their numbers have now swelled to an estimated 100,000. The aquatic rodents, which have thrived in the absence of native predators, have invaded roughly 16 million hectares of unique, indigenous forest, leaving a swath of destruction “that is absolutely stunning — it looks like bulldozers steamed through”, according to ecologist Josh Donlan, director of Advanced Conservation Strategies, a non-profit organization based in Driggs, Idaho.


This info and more at; http://www.nature.com/news/2008/080618/full/453968a.html