Alien vertebrate risk assessment and invasion pathway modelling

Alien species are a key driver of the ongoing biodiversity crisis. Changing patterns in the number and identity of transported alien species, and recent changes in the importance of different pathways for transporting alien species (e.g., recent decline in the role of acclimatisation societies vs. the increase in importance of the pet trade), means that there is a novel pool of alien species available for introduction. There is a pressing need to evaluate the biosecurity risks posed by these emergent alien species and their pathways. In this thesis, I focussed on unravelling the patterns and processes driving the transport, introduction, and establishment of novel vertebrate taxa (e.g., alien amphibians, reptiles, and fishes) in Australia and the world. Complementarily, I have also developed approaches to support the implementation of early detection activities for emergent alien reptile species. My results have highlighted the large number of new alien vertebrates being transported around the world, and particularly in Australia. The wildlife trade transports a substantial portion of all alien vertebrates, whereas unintentional pathways (i.e., stowaways) move fewer numbers of alien vertebrates (in terms of species transported). My research found that propagule number, the minimum number of release events of an alien species, is the main predictor of establishment success of self-sustaining reproductive alien populations. My global analysis of the relationship between the trade in Nearctic pet turtles and their establishment success revealed the complexities associated with managing novel pathways. The probability of introduction of a turtle species in a country (release or escape into the recipient environment) relates to the number of turtles imported, whereas the probability of establishment was associated with propagule numbers (number of releases) but not the number of individuals imported. My research on the establishment of alien fishes in Australia demonstrated substantial modern changes in the importance of transport pathways, with the recent rise of the ornamental fish trade as the key source of new alien species. These shifts in the importance of pathways for alien fish transport have also altered the processes governing the establishment success of alien fishes in Australia. The prevention of the establishment of new alien species is the best course for managing their potential impacts. However, even the best of prevention strategies cannot realistically aspire to be perfect. In order to be successful at preventing new alien species, it is important to implement early detection systems. I have developed and evaluated a quantitative approach for the early detection of alien reptiles on Christmas Island. The results indicate that large surveying efforts have to be conducted to ensure the absence of new alien reptiles with confidence. Drawing from the results of my research, I conclude with some suggestions to improve preventive management strategies for alien species. Particularly, I argue in favour of incorporating economic considerations in prevention strategies (e.g., the benefits of early detection activities vs. delayed intervention and eradication), conducting further research into the importance and drivers of different transport pathways, and examining potential management alternatives to species-based risk assessments.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Biological Sciences, 2017