From AmphibiaWeb News:
What distinguishes invasive amphibian species at the earliest stage of becoming invasive?
Tingley et al. (2010) found that introduced amphibian species were biased taxonomically, with about 50% of introduced species coming from only 3 families: Hylidae, Ranidae, and Salamandridae. Introduced amphibian species were primarily from the Northern Hemisphere. As has been found for introduced mammals, birds, and fish, introduced amphibians had a broad geographic range and were associated with locations having high human density. Large species were more likely to have been transported intentionally, while smaller species were more likely to have been stowaways. Large species also tend to have life history traits associated with successful invasion (high fecundity, mobility, etc.). Ninety percent of caudate introductions were found to be intentional.