Patterns of transport and introduction of exotic amphibians in Australia
Research on amphibian invasions has largely focused on the likelihood of successful establishment, while analysis of the previous stages in the invasion pathway (transport and introduction) is scarce despite its critical importance. Here, we investigate the patterns of taxonomic and geographic non-randomness as well as the factors affecting the transport and introduction of amphibians.
We compiled and analysed a database on the identity of transported and introduced amphibians. First, we tested for taxonomic (family level) and geographic non-randomness by comparing transported and introduced species with all extant caudates and anurans. Second, we constructed models to examine the influence of different factors upon the probability of transport and introduction of amphibians in Australia.
Amphibians were transported via two main pathways: trade (71 species) and stowaway (38 species). In addition, several species were transported through both pathways. Transported species represented a taxonomic and geographic non-random sample of all extant amphibian species. Conversely, introduced species constituted a random sample of the transported amphibians. Regardless of the transport pathway, the probability of transport of amphibians increased with increasing extent of their native geographical range. A large number of native Australian species have been transported outside their naturally occurring ranges, representing over 65% of the introduced species. Introduction is strongly correlated with the transport pathway, that is, species transported through two pathways were more likely to be released or escape from captivity.
The probability of amphibians being transported and introduced to, or within, Australia is critically affected by their availability to be captured, bred and housed in captivity. Management strategies to prevent the future introduction and establishment of new amphibians need to include the people involved in species trade, as well as continued vigilance by biosecurity and custom agencies.