Impacts of climate change on high priority fruit fly species in Australia

cells assigned 0 when unsuitable and 1 when suitable) for each time period were summed to produce a consensus map, identifying agreement about the suitability of grid cells across the six climate scenarios. Each species’ consensus map was then converting to a binary map indi- cating whether cells were projected to be suitable under the majority of GCMs (i.e., suitable in < 4 GCMs = 0, suitable in 4 or more = 1). The resulting binary maps were summed across species to identify hotspots—grid cells suitable for multiple pest species. Finally, we compared the distribution of hotspots to that of major horticultural crops. When projecting models, extrapolation to conditions beyond the range of the training data may be unreliable. Following Elith et al. [53] we developed MESS (multivariate environmental similarity surface) maps to identify regions of extrapolation [53]. By revealing areas with novel environmental conditions, MESS maps can be used as a projection mask, highlighting regions for which less confidence can be placed in projections, or as a quantitative measure of predic- tion uncertainty [53]. We then recalculated the size of projected suitable climate with novel environments excluded. All modelling and post-modelling analyses and calculation of statistics were performed in R version 3.1.2 [46]. We used the sp [54] and raster [55] packages for preparation and manipula- tion of spatial data, the dismo [56] package to fit Maxent models, and custom R code for rapid projection of fitted models. Results Model performance

Model performance for all species was better than random, with average cross-validated AUC ranging from 0.815 (SD = 0.05; B. frauenfeldi) to 0.907 (SD = 0.02; B. neohumeralis) (S1 File). Bactrocera aquilonis. Our model suggested that, during the baseline period, climatically suitable habitat for B. aquilonis existed in the northern regions of the Northern Territory and Western Australia, as well as northern Queensland where this fly has not been reported (S1 File). The variables with the highest permutation importance were precipitation of the wettest quarter (68.9%) and annual mean temperature (28.9%) (S1 File). As the century progresses, the geographic extent of climatically suitable habitat for this spe- cies is projected to increase and expand southwards under all six scenarios, with many areas suitable in the baseline period projected to remain so until at least 2070 (S1 File). This includes northern Western Australia, much of the Northern Territory, and north-western Queensland (S1 File). We note, however, that climate scenarios beyond 2030 frequently contain novel con- ditions across the northern regions of Australian, highlighting uncertainty in Maxent projec- tions within these areas (S1 File). Key horticultural crops for B. aquilonis are Mangifera indica (mango), Citrus × paradisi (grapefruit), Malus domestica (apple), Prunus persica (peach) and Citrus sp. (citrus) (S1 File). The major regions where these crops are currently grown include the Northern Territory and north-east Western Australia. These regions may remain suitable for B. aquilonis until at least

2070. Similarly, fruit growing regions in the Wet Tropics (north-east Queensland) are likely to increase in suitability in the future. Other major host-plant growing regions in the south and east of the continent will likely remain unsuitable (S1 File). Bactrocera bryoniae. Suitable habitat for B. bryoniae during the baseline period is pro- jected to have occurred along the northern and eastern coastlines (S1 File). Temperature annual range and precipitation of the driest month contributed the most to the model for this species (42.2% and 27.4%, respectively) (S1 File). By 2070, suitable habitat is projected to increase under all scenarios except GFDL-ESM2M (which projects a hot, very dry future) (S1 File), expanding to the southern coastlines of Impacts of climate change on high priority fruit fly species in Australia PLOS ONE | https://doi.org/10.1371/journal.pone.0213820 February 13, 2020 6 / 19