For years, ecologists have been fretting that foreign species contaminate unique ecosystems. Their fear makes sense: It's easy to see why bringing a family of hungry lions to a small island filled with herbivores might cause serious difficulties.
But newly introduced species may be able to get along with their native brethren better than previously believed. In August the ecologists Dov Sax of Brown University and Steven Gaines of the University of California at Santa Barbara published a study in the Proceedings of the National Academy of Sciences looking at the effect of invasive species on extinction of native species. They found that, in general, introducing exotic species to oceanic islands increases their overall biodiversity.
What's more, with the exception of birds, there is very little evidence that invasive species are causing native species to go extinct. New Zealand, for example, is home to more than 2,000 native plant species. Since the arrival of human beings more than 2,000 additional plant species have spread across the local landscape, and only three native plant species have gone extinct.
In fact, thanks to humanity's penchant for shuffling species around the globe, the species richness of most ecosystems is increasing. The researchers point out that on many oceanic islands biodiversity has doubled in the last two centuries. Of course, there are other reasons to bemoan the introduction of certain species: Few welcome the increase in biodiversity brought to North America by the introduction of Japanese beetles and tiger mosquitos.