The authors Dov F. Sax, assistant research scientist at the University of California, Santa Barbara; Steven D. Gaines, director of the Marine Science Institute and acting vice chancellor for research at UCSB; and James H. Brown, professor of biology at the University of New Mexico studied data collected on oceanic island land birds and plants. Records from islands are useful because they present discrete areas where additions and subtractions of species can be accurately determined.
The article, "Species Invasions Exceed extinctions on Islands Worldwide: A Comparative Study of Plants and Birds," documents the fact that "land birds have experienced massive extinctions on oceanic islands, with many islands losing more than half of their native species," said Gaines. "On these same islands, however, many exotic bird species have become established, such that the total number of land bird species has remained relatively unchanged." (Exotic species are those that are native to one region and have been introduced to another; they can reduce diversity by causing extinctions of native species. However, they also increase diversity by adding to the total number of species in a region.)
Lead author Sax said, "We may be headed for a sort of biotic homogenization, with the same species everywhere. Lose a parrot, get a starling; no one wants that."
Gaines said that while few native plant species have gone extinct, vast numbers of exotic species have become established, according to the island data. As a result, the number of plant species has increased greatly approximately doubling the total number of spe
Contact: Gail Gallessich
University of California - Santa Barbara