RENO, Nev. - A leading ecologist warned Tuesday that the invasion of non-native plant and animal species rivals global warming's threat to world ecosystems.
''Most people think about temperature and climate when they think about global change,'' said Harold Mooney, an environmental biologist at Stanford University.
''But equally important is biological change,'' he said in a speech at the Desert Research Institute, which just named him the winner of its most prestigious annual research award.
''The invasion of species is a great threat to biodiversity. They have totally altered ecosystems and their structures ... And the sad thing is, this problem will get worse.''
From the brown tree snake of Guam, to the cheatgrass that is overtaking sagebrush ecosystems in the Great Basin and the marine species invading the Great Lakes, non-native species pose threats to entire economies, Mooney said.
Economists at Cornell University estimate invasive species cause environmental damages and losses totaling $138 billion a year, he said.
An estimated 2,000 plant species and 2,000 insect species have been introduced into the United States since trade began here more than 200 years ago, Mooney said.
The acceleration of new species in recent years is the most cause for alarm, he said.
In San Francisco Bay from 1851-1960, one new species was introduced on average every 55 weeks. But from 1961-95, the rate increased to one every 14 weeks, he said.
In Hawaii, ''we now have as many new things as things that evolved there,'' Mooney said. ''The whole biological landscape is very different than it was a couple hundred years ago.''
Mooney is a member of the National Academy of Sciences and former president of the Ecological Society of America. He was awarded the institute's 2000 Nevada Medal - a silver medallion and $10,000 prize presented to a national leader in science or engineering.
Protests at the World Trade Organization meeting in Seattle sent an important message ''that some of these environmental issues related to trade need to be addressed,'' Mooney said.
''All the continents have been put back together'' as a result of the global economy and the modern air and shipping routes that connect them, he said.
Mooney said he'd like to see the WTO change the burden of proof so that someone shipping an exotic plant or animal into another country would have to ''demonstrate it won't do any damage before you let it in.
''The way the rules are written now, in order for a nation to block something from coming in they have to show it will cause damage,'' he said.
''Science isn't up to that task. We can't predict when and where invasions will occur. ... And what we have to lose is too great,'' he said.
Mooney said the problem with cheatgrass overtaking sage brush in Nevada and other parts of the West ''isn't peculiar to here.''
It's typical of other places in the world where woody vegetation - in this case sagebrush - is cleared off the land as the result of some disturbance, he said.
Grasslands that are more susceptible to fire replace the vegetation and in turn catch fire, burning more of the woody material and replacing it again with more grasses, and so on in a cycle, he said.