Vertebrates in trade that pose high invasion risk to the United States

The United States imports thousands of live vertebrate species annually as part of legal trade. Escapes and releases from captivity are major pathways of invasion, however, the risk posed by the thousands of imported vertebrate species has not been systematically assessed. We conducted a horizon scan that used a data-driven climate match to filter a list of nearly 15,000 taxa drawn from across the globe of imported fish, amphibians, reptiles, birds, and mammals for rapid assessment by taxonomic experts. Experts evaluated 840 species and identified 32 (22 reptiles and 10 fishes) as having the highest risk for establishment, spread, and negative impacts. Of those high-risk species, the majority have the capacity to disrupt ecosystem processes via their role as top predators or the unique ecological niches that they occupy, while several of the snake species pose a threat to human health. High-risk species were often scored with high confidence while in contrast, low scores were attributed to a combination of ecological redundancy, low propagule pressure, or low climate match while low confidence arose from a lack of information in the literature (i.e., data deficiency). Our study therefore highlights legally imported species likely to cause the greatest harm with the recognition that many other species could also become invasive in the United States. The ranked list of vertebrate threats can be used to prioritize watchlists and inform the development of targeted regulations for importation can be applied to regions to provide a rapid, preliminary screening for large pools of potential invaders.