Washington

Spend now to save later — that's the message from biologists Brian Leung and David Lodge, who have made what they say is the first attempt to merge ecology and economics into a mathematical model for analysing the risks from invasive species.

Leung and Lodge, who are based at the University of Notre Dame in Indiana, used zebra mussels as a test case. These molluscs cost US industry about $100 million a year, primarily by clogging pipes and reducing water flow to lake-side power plants.

The researchers modelled the rate at which the invaders spread and weighed up the economic factors involved, such as the costs of preventing the mussels from invading new lakes. They calculate that it is worth spending up to $324,000 a year to stop zebra mussels from contaminating a lake with a large power plant (B. Leung et al. Proc. R. Soc. Lond. B; in the press). As the US Fish and Wildlife Service spends just $825,000 a year controlling all non-indigenous aquatic species in the country's lakes, Leung and Lodge conclude that “a much higher value should be placed on prevention”.

Environmental economics is still a relatively new field, but quantitative tools such as this may help policy-makers to decide when it pays to prevent the spread of invasive species, says Lodge. “These sorts of analyses just haven't been done,” he says, even though damage caused by invasive species costs the United States about $137 billion a year.

With no similar studies available, it is unclear how widely Leung and Lodge's results can be applied. But their model suggests that, for zebra mussels at least, the problem should not be ignored. Over five years, it showed that it was cheaper to do nothing. But for 25 years, the economic benefits of prevention were clear.