Introduced species can wreak havoc on the ecosystems they invade. But what happens after they've been established for centuries? A new study in the latest Proceedings of the Royal Society suggests that, in one case, an introduced species has actually become an important part of the native ecosystem -- and helps protect native species from another invader [$-a]. ... Recently a news article in Nature discussed ragamuffin earth [$-a] -- the idea that human interference in nature has so dramatically changed natural systems that it may often be impossible to restore "pristine" ecological communities. In these cases, some ecologists say, conservation efforts might be better focused on how to maintain and improve the diversity and productivity of the novel ecosystems we've inadvertently created. It looks as though the dingo could be a poster child for exactly this approach.
The havoc that introduced species have caused in some areas is well known, such as Australia (most prominently, but limited to, rabbits). But the term "invasive" seems more a normative than a scientific one, after all,
at some point endemic species were invasive.
For example, the "pristine" ecosystems of North American before Europeans arrived were certainly reshaped in the last 10,000 years by the migration of Old World species such as bison and the gray wolf, combined with human predation and utilization of fire. In fact recent research hints that the "virgin" Amazon rainforest may actually have taken up its present form after the die-off of native populations within the last 300-400 years.