The trade in live vertebrates as an invasion pathway

The trade in live vertebrates has been identified as an important pathway for vertebrate introduction.  However, theory suggests that the probability is small that a given species transported to a new range will be introduced and subsequently establish.  Identifying those species that do transition through the transport and introduction stages can be difficult.  Vertebrate importation data maintained by the United States Fish and Wildlife Service provide a method to quantify the species and individuals that have been transported to the United States.  Using these data for several taxonomic groups (amphibians, turtles, lizards, snakes, and birds), I report an analysis of current and historical importation effort and whether these data capture the vertebrate species that have transitioned from the transport to the introduction stage in the United States.  I found that the proportion of species imported that transitioned to the introduction stage ranged from 2 to 10%, and the proportion that transitioned from the introduction to establishment stage ranged from 15 to 35%.  These results provide a baseline for the proportion of imported vertebrate species that will be introduced, and suggest that the US Fish and Wildlife data are an informative source that can be used to assess these transition stages in the invasion process.