About 170 invasive alien species have colonized the Great Lakes, causing both ecological and economic damage. Some species, such as zebra mussels, attach to every available surface, smothering other animals and clogging intake pipes of power plants. Others, such as the sea lamprey, shoulder native species aside, competing with and often attacking them, ecologist David Lodge of the University of Notre Dame, Indiana, told an audience here at the annual meeting of the American Association for the Advancement of Science, publisher of ScienceNOW.

To find out why some invasive species can overrun a new ecosystem, Lodge and graduate student Cynthia Kolar examined the fates of species that had reached the Great Lakes. Of 40 different fish species that had been introduced into the lakes, 25 had colonized successfully, and 15 had never come to call the Great Lakes home. The researchers isolated four qualities that could predict, "with over 90% accuracy," Lodge says, which fish species would thrive in their new digs: whether the species could survive in 4°C water; whether the species had a history of invading other places; the fishes' age at maturity; and how many of and how often the fish had been introduced.

With these factors in hand, the researchers then made predictions about which species are likely to be a threat in the future. The team applied the criteria to 68 fish species native to the Ponto-Caspian basin, an area that has served as a source of many of the Great Lakes' current exotic species. Most of the invaders are thought to have hitched a ride in ships' ballast water. Twenty-three of those 68 species would be capable of colonizing the Great Lakes, the team predicts. "These are the first quantitatively based freshwater predictions for invasive species," says Lodge.

Harold Mooney, an ecologist at Stanford University, says that Lodge's work is an important stepping stone because "he can now tell us the likelihood of something becoming established." Mooney urges others to follow Lodge's lead and create predictive invasion models for other ecosystems and groups of organisms. Meanwhile, Lodge is using a similar strategy to predict which plants and invertebrates are poised to invade the Great Lakes.

--MARI N. JENSEN