Abstract
Although currently exotic to New Zealand, the potential geographic distribution of Amblyomma americanum (L.), the lone star tick, was modelled using maximum entropy (MaxEnt). The MaxEnt model was calibrated across the native range of A. americanum in North America using present-day climatic conditions and occurrence data from museum collections. The resulting model was then projected onto New Zealand using both present-day and future climates modelled under two greenhouse gas emission scenarios, representative concentration pathways (RCP) 4.5 (low) and RCP 8.5 (high). Three sets of WorldClim bioclimatic variables were chosen using the jackknife method and tested in MaxEnt using different combinations of model feature class functions and regularization multiplier values. The preferred model was selected based on partial receiver operating characteristic tests, the omission rate and the lowest Akaike information criterion. The final model had four bioclimatic variables, Annual Mean Temperature (BIO1), Annual Precipitation (BIO12), Precipitation Seasonality (BIO15) and Precipitation of Driest Quarter (BIO17), and the projected New Zealand distribution was broadly similar to that of Haemaphysalis longicornis Neumann, New Zealand’s only livestock tick, but with a more extensive predicted suitability. The climate change predictions for the year 2050 under both low and high RCP scenarios projected only moderate increases in habitat suitability along the mountain valleys in the South Island. In conclusion, this analysis shows that given the opportunity and license A. americanum could and would successfully establish in New Zealand and could provide another vector for theileriosis organisms.
Highlights
New Zealand’s relative geographic isolation has not prevented the self- or assisted introduction of many exotic species of plants and animals (McGlone 2006; Williams and Cameron 2006)
The projected distribution for A. americanum shown in Fig. 2a closely matches that known for H. longicornis in New Zealand, parts of the South Island that are predicted as suitable for A. americanum are slightly more extensive than those currently predicted as a possible extension of the range of H. longicornis (Lawrence et al 2017)
The annual mean temperature is the average monthly average temperature, the annual precipitation is the sum of all the monthly rainfall, the precipitation seasonality is the ratio of the standard deviation of the monthly rainfall to the average monthly rainfall and precipitation of driest quarter is the total rainfall for the driest consecutive months
Summary
New Zealand’s relative geographic isolation has not prevented the self- or assisted introduction of many exotic species of plants and animals (McGlone 2006; Williams and Cameron 2006). With tourism recently edging out dairy as New Zealand’s biggest export earner, it is in the best interests of the country to promote itself as safe for visitors. This requires that potential human exposure to parasites and disease organisms is kept to a minimum. In an effort to maintain barriers against unwanted organisms, biosecurity measures are in place such that incoming passengers are screened for unwanted materials that might introduce exotic diseases and pests. Mosquitoes, fleas, parasitic mites and ticks are examples of medical and veterinary arthropod pests that are regularly encountered, the only livestock tick in New Zealand, Haemaphysalis longicornis Neumann, invaded and established long before any comprehensive quarantine measures were in place (Myers 1924). Of considerable contemporary interest is the finding of H. longicornis in north-eastern USA (Rainey et al 2018) showing that it and many other species of ticks (Burridge 2011) are still threatening invasion around the globe
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