Forecasting biological invasions with increasing international trade

We used historical data to parameterize species-accumulation models relating international trade to the establishment rates of nonindigenous species in the United States over the past century. We then coupled these relationships with published trade forecasts to predict future invasion rates for insects, plant pathogens, and mollusks. Relationships between the accumulation of non-native species and merchandise imports were reasonably described by log-log and log-linear species-area models and Michaelis-Menten accumulation functions. However, the latter two models produced markedly better fits. When coupled with projected trade forecasts, the log-linear species-area model predicted 16-24% taxon-specific increases in the number of nonindigenous species established in the United States from 2000 to 2020. The Michaelis-Menten model predicted much lower 3-6% increases, but even this meant 115 new insect species and 5 new plant pathogens. These results suggest that the ecological and economic costs associated with human-caused biological invasions may continue to rise substantially over the coming decades.