The globalization of trade and travel continue to increase the number of species moved beyond their native range, and the speed at which they are delivered to new ecosystems. Risk assessment at the species level is increasingly being used to screen species in trade to determine the invasion risks posed. However, the sheer number of species in trade means that the capacity for risk assessment is often insufficient to assess all incoming species. This has lead to a search for rapid risk assessment protocols based on easily available data. The two factors most commonly predictive of future invasion are whether a species has a climate match to the new ecosystem, and whether the species has a history of invasion elsewhere. We have tested this risk assessment framework by applying it retroactively to occurrences of non-native fishes in the United States. For each non-native species recorded, we have determined whether it has become established or died out, whether it has a climate match to the US based on latitudinal overlap, and whether it was established elsewhere at the time of US introduction. These analyses have been conducted at the scale of the continental US, and regionally.
Results/Conclusions
A total of 154 species of non-native freshwater fish species have been recorded from the continental United States. Of these, 81 failed to establish, 27 established without impacts, 17 established with minor impacts, and 29 established with major impacts. The percentage of species established elsewhere prior to their discovery in the US was lower for species that failed to establish (22%), or that have become established with no impacts (22%), than for species that have become established with minor (59%) or major (76%) impacts. Likewise, a trend exists with climate match, with non-establishers (42%) and establishers without impacts (37%) less likely to have a climate match than those species established with minor (77%) or major (66%) impacts. Applying these two traits in a rapid risk assessment would have correctly predicted the invasion status of 75% of introduced fishes, and sometimes higher in certain regions. Although this is lower than for some risk assessment tools, the lack of data available for many of these historical introductions means that risk assessment conducted on contemporary introductions could be more accurate. This demonstrates that rapid risk assessment may be a usefully quick, accurate tool for identifying species that pose high risks of invasion.