Exotic species swapping: Reciprocal movement of animal species among regions of the Americas

The movement of exotic species, both intentional and unintentional, is among the top threats to global biodiversity and native taxa. Research has frequently explored species movement between the eastern and western hemispheres, focusing on the number of species moving from east to west. Here we use qualitative and quantitative information from a compiled exotic species compendium (CABI Digital Library) to produce a conservative picture of the exchange of nonnative animal species, trends in movement of various taxa among regions, and the trade relationships that could contribute to species’ movements strictly within four major regions of the western hemisphere (North America, South America, Central America, and the Caribbean). Species exchange between regions in the western hemisphere (285) were higher than documented invasions from all regions of the eastern hemisphere with the exception of Asia, the largest region in the study (348). Among the broad taxonomic categories, arthropods and fish dominated the counts of exchanged species in every region, largely due to trade related to food production, aesthetics, or sport. Perhaps due to the importance of trade-related movement vectors for the dominant taxa, country GDP was positively related to export of exotic species. Therefore, the magnitude and importance of species exchanges among countries in the western hemisphere has been underestimated, with factors like proximity and economic trade connections likely leading to more species translocations.