CORVALLIS, Ore. - Plant and animal diseases can play a major and poorly appreciated role in allowing the invasion of exotic species, which in turn often threatens biodiversity, ecological function and the world economy, researchers say in a new report.

In particular, a plant pathogen appears to have opened the gate for the successful invasion of non-native grasses into much of California, one of the world's largest documented cases of invading species and one that dramatically changed the history and ecology of a vast grassland ecosystem.

The study, published today in Proceedings of the National Academy of Sciences, a professional journal, should improve the understanding of invasive species and possibly suggest new tools to combat them, said researchers at Oregon State University.

"Even if we can't control all the diseases that help species invade, at least now we know to consider diseases when studying invasion," said Elizabeth Borer, an assistant professor of zoology at OSU. "In analyzing the ecology of exotic plant or animal species, it's clear that diseases are one part of the equation."

About 50,000 exotic species have been introduced into the United States, and the havoc they wreak upon agricultural crops, wildlife, ranch animals, forests and grasslands costs about $137 billion a year, scientists say. Invading species are also responsible for about half of all native species that go extinct, studies show.

One of the primary theories of successful invading species, experts say, until now had been the "enemy release hypothesis," in which an invasive species is no longer constrained by whatever predators or control mechanisms kept it in check in its native habitat.

The new study, however, suggests diseases that are native to a region, or imported along with invasive species, may also play a key role in whether or not the invader becomes a significant problem.

In the case of California, some
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Contact: Elizabeth Borer
borer@science.oregonstate.edu
541-737-3701
Oregon State University
12-Mar-2007