Abstract:
Invasive ants can have negative impacts around the world on natural ecosystems and horticultural industries. The invasion pathway is seldom studied in its full extent (from pre to post border) when considering taxa, mostly one specific part of the pathway is explored in great detail, as has been done with exotic ants establishing in New Zealand. Exotic ants are an excellent case study of invasive species in New Zealand; they are frequently intercepted entering New Zealand‘s border and there are excellent digitised location records from around New Zealand representing their spread. This study explores three stages of the invasion pathway for exotic ants in New Zealand : i) the pre-border transportation/vectoring stage, where the diversity, interception rates, and origins, of ant species and genera entering New Zealand were examined using border interception rates; ii) the establishment stage where a range of variables were modelled to examine why some species and genera overcome the barriers of establishment and why others cannot; and iii) the spread stage, where the variables used in the establishment stage were modelled to describe the spread rate of species, at both a micro and macro resolution, as well as determining which habitats are most likely to be invaded. Two datasets were compiled: i) border interception records obtained from the Ministry for Primary Industries and published literature to explore ants entering New Zealand as well as to predict exotic ant establishment; and ii) natural history collection records from entomology collections around New Zealand to determine the spread rates and habitation variables of exotic ants already established. For border interceptions, data contained 5932 records at the species level for 146 different species. Species diversity remained consistent over time, however, one species, Pheidole megacephala, dominated these records (20.4%), and twenty of the 146 species represented 90% of the records. Reproductive ability was the only variable to markedly change using information about the caste and type of interception, showing a marked decrease over time from 82% to 26%. Linear Discriminant Analyses correctly predicted the failure of a species to establish 87.2% of the time using the variables of hind tibia length, minimum temperature (of the most extreme global locality), mean temperature (of the most extreme global locality), and interception rate. However, this model only correctly predicted establishment 39% of the time. At the genus level, models were able to correctly predict establishment success at 76.4% and failure to establish at 78.9%. Two variables, interception rate and cold temperature tolerance (minimum temperature), were important predictor variables for the establishment phase significantly increased both minimum and maximum spread rates. Human-modified habitats had the highest occupancy of exotic ant species, with the highest number of records being found within urban environments. Both of these establishment variables were also significant factors at the spread phase. These results can be used in the augmentation of existing risk assessment or in the implementation of new risk assessment analyses and mitigation methods.