exotics and diversity

From the NY Times, some exciting research on the effect of introduced, exotic organisms on native species. We all have the impression that this is an ongoing catastrophe, but this is not necessarily so. Introduced predators sometimes wipe out native species by eating them, but otherwise introduced species rarely cause the extinction of natives.

As the authors of the study point out, 2,069 species of non-native plants have become established in New Zealand, and this has led to the extinction of exactly three native species. The net result of the introduction of new species has been a doubling of the number of wild plant species in the islands. Some native species have become much rarer, but that does not necessarily mean they will become extinct.