Certainly, they say, non-native plants and critters can be terribly destructive—the tree-killing gypsy moth comes to mind. Yet natives such as the Southern Pine Beetle can cause similar harm. The effects of exotics on biodiversity are mixed. Their entry into a region may reduce indigenous populations, but they're not likely to cause any extinctions (at least on continents and in oceans—lakes and islands are more vulnerable). Since the arrival of Europeans in the New World, hundreds of imports have flourished in their new environments.Tuhus-Dubrow cites the case of Tamarisk in the U.S. Southwest -- an aggressive introduced shrub that has also ended up providing important nesting sites for the endangered southwestern willow flycatcher.
The fact of the matter is that human-introduced species can eventually integrate into an ecological community; once they do it's hard to get them out, and problematic as to whether it's a good idea. In Australia, dingoes helped extirpate many other large predators when they were introduced by the first humans to arrive on that continent -- and now they're critical to controlling other, later-introduced mammal species.
(Thanks to Ephraim Zimmerman for point this one out to me!)
Invasive pest, or critical flycatcher habitat? Maybe both. Photo by Anita363.