Boring Beetles and Super Models: Mapping Potential Distributions of a New Invader

ABSTRACT Aim Predicting the potential distribution of an invasive species is critical for informing decisions around surveillance, containment and eradication. Mechanistic species distribution models directly describe how aspects of the environment affect organismal fitness through space and time. These models also provide insight into population dynamics, such as rates of population growth and spread. Here, we develop a temperature‐dependent stage‐structured population dynamic model for a globally significant invader, the polyphagous shot hole borer (PSHB). We use this model to predict the beetle's potential distribution across its invaded range. Location Australia, South Africa, USA, Israel, South America. Taxon Euwallacea fornicatus . Methods We synthesise previous studies to parameterise our population dynamic model, estimating population growth as a function of temperature within a host tree. We ran the model over 1 year using daily climate data across regions with invasive PSHB populations. To make predictions over large spatial scales, we ran the model using the Pawsey supercomputing system. Habitat suitability was mapped according to population growth (and, in Australian simulations, host tree availability). We also used the model to estimate the mortality of adults during between‐host dispersal (an uncertain parameter) and to predict spread rate. Results Distribution maps indicate that PSHB currently occupies the most climatically suitable parts of California and Israel, but is yet to invade the most suitable regions in Australia, South Africa and South America. The model shows the species is capable of very high population growth. We estimated that for current populations to persist, the loss through between‐host dispersal mortality needs to be < 40%. The maximum spread rate (discounting transport by humans) was estimated to be 3.75 km/year. Main Conclusions PSHB causes serious damage to urban and agricultural trees, and the continued expansion of its global distribution is a major concern. Our model provides insights into the spatial and temporal heterogeneity of invasion risk, to assist global efforts to manage the ongoing invasion of this species. Predictions could be further honed with the availability of more comprehensive datasets on PSHB life history, internal tree temperatures and host tree distributions.