Check out 1491 by Charles C. Mann, where he talks about the kinds of ecosystem impacts that indigenous societies made for thousands of years before the Europeans showed up in the Americas. He cites intriguing evidence that huge swaths of the Americas were farmed by populations in the millions spread throughout what we think was "pristine" wilderness. Mann argues they had figured out pretty well how to do sustainable agriculture (although periodically hit with internal wars and severe droughts resulting in abandoning sites). Tragically, the people of the Americas had no immunity to the plagues of diseases they encountered from the Europeans. With their numbers incredibly depleted they could no longer conduct sustainable agriculture and previously cultivated land and animal populations changed into what later colonists perceived as the "natural" wild state to which so many are clamoring to "return" to now. Mann explains how humans had shaped nature from the beginning.
As noted in my earlier post, humans are major players in the ecosystem. Whether we make good choices on how we effect changes to our ecosystem is up to us. For we have and will continue to change the world.