encouraged and supported among scientists with taxonomic expertise and those who specialize in population biology, community ecology, epidemiology, and simulation modeling. Multidisciplinary training of established and new investigators is needed to provide the expertise needed to make the study of invasion biology predictive.

In spite of a long history of interest in biological invasion, scientific inquiry in invasion is still nascent. Progress in understanding and predicting invasions will depend on how well the insights of investigators with diverse training can be coalesced and directed to decipher the myriad combinations of immigrant species, new ranges, and novel circumstances that can produce a biological invasion. The last 10 years has seen the emergence of a broad consensus that the prediction of biological invasion is a field of pressing national need. It will take some time, however, to generate the predictive principles on which policy-makers, regulators, the scientific community, and the public can have confidence.

Driving this sense of urgency is the growth in world trade of commodities and propagated material. The increasing volume of trade and the growing number of nations that are linked routinely to the United States through trade will undoubtedly result in the delivery of more nonindigenous species than ever before to U.S. ports of entry. With little or no biological information about these species that can be translated into risk assessment and prediction, APHIS will have difficulty evaluating and regulating them. The challenge of constructing a scientific basis for predicting the risk associated with nonindigenous species needs to be met by a significant national effort, including other agencies within the USDA, other branches of the federal government responsible for research and land management, agricultural and natural resource agencies of state governments, and the scientific community at large.