The CLIMEX model developed for TPP provides essential information about the directions and likely changes in the pest’s potential climatic suitability under current and future climate changes. TPP is projected to persist well in a range of climatic conditions, including hot and cold semi-arid, Mediterranean, temperate savannah, tropical savannah, continental, and oceanic climates. Under current climate models, heat stress and wet stress are the major limiting factors preventing the potential establishment of this species in the tropical rainforest or hot-wet climates, while cold stress limits their survival in subarctic climates. Our model matches well with the current known distribution of TPP in its native (USA and Mexico, Guatemala, and Honduras) and invasive (El Salvador, New Zealand, and Australia) ranges. Additionally, the model suggests that TPP has the potential to expand into other continents such as South America, Europe, Asia, and Africa. Our results closely agree with potential distribution projections made by Wan et al. 2020 using MaxEnt. Both MaxEnt and CLIMEX are widely used ecological niche modelling tools to predict species distributions effectively (Byeon et al. 2018; Huang et al. 2019; Liu and Shi 2020). The MaxEnt software is used to find the maximum entropy distribution probability to predict potential distributions considering the primary climate variables that affect the target species. It uses information on sampling locations of the target species and environment variables (Phillips et al. 2006). The CLIMEX software provides more opportunities to use species-specific biological data for the model and climatic variables at dynamic daily and weekly intervals (Sutherst et al. 2007). However, potential distribution maps are similar in their coverage of geographical range, and both niche modelling tools have identified Eurasia, North and South America, Africa, and Australasia as climatically suitable regions. However, there are substantial differences in climatic suitability classes predicted by the two models due to variation in defining particular aspects of suitability. CLIMEX uses EI or an Ecoclimatic Index to categorise the climatic suitability (Kriticos et al. 2015). In contrast, AUC or the average area under the curve is used in MaxEnt (Byeon et al. 2018).
A climate change scenario simulated for the year 2090 showed an overall significant contraction of the potential distribution of TPP and changing suitability classes from higher to lower climatic categories. Shifts in the known distribution of species are expected to result from climate change (Harrington et al. 2001; Van der Putten et al. 2010; Visser and Holleman, 2001; Walther et al. 2002; Yukawa et al. 2007). Our model projections in a climate change scenario showed apparent poleward range shifts, which match predicted hot-summer continental climates at higher latitudes in the future. However, TPP’s distribution in the Mediterranean and oceanic climates will remain relatively unchanged in the future with climate warming, including in the UK, France, Switzerland, the Netherlands, Germany, Poland, and Italy.
New Zealand will be more climatically favourable in the adventitious region, while Australia will be less favourable for TPP’s survival under a future climate change scenario. The future predicted climate in New Zealand is expected to provide more suitable conditions for TPP, except in alpine regions in the eastern and southern parts of the South Island.
Both of our CLIMEX models (i.e. current and future climate scenarios) will provide valuable information to develop or improve the current management strategies for TPP. Our model showed that the world's largest-scale potato producers (i.e. China, Russia, Ukraine, Germany, France, Poland, and the Netherlands (FAOSTAT 2021), which are currently free of TPP, are expected to have optimal and high climatic suitability for TPP under current climatic conditions. Therefore, the information provided from our model’s predictions can assist biosecurity authorities in developing appropriate strategies to manage the risk posed by this invasive species. Authorities in high-risk countries may evaluate options to strengthen biosecurity measurements to prevent pest entry. Whereas New Zealand, for example, could use the model predictions to develop future pest management strategies as TPP is an injurious pest to control with current management practices (Vereijssen, 2020).
It is paramount to have a thorough understanding of all variables that may define the geographical distributions of invasive species when attempting to predict their current potential range and future dispersal (Taylor and Kumar 2013). For example, host availability, dispersal capacity, competition, the effect of natural enemies, habitat preferences, and landscape can have significant roles in defining the new geographical range of invasive species once they have arrived in a new environment (Patrick and Olckers 2014).
CLIMEX and other niche modelling software have some restrictions since they only use climate-related features and meteorological data and do not incorporate non-climatic factors, such as dispersal capacity and host availability when modelling predictions (Baker et al. 2000; Kriticos et al. 2015; Saavedra et al. 2015). Nevertheless, the models presented in this study have provided valuable information on the potential and future geographical distribution of TPP globally. This information can be used to assist biosecurity programmes such as identifying high-risk areas and potential entry pathways, designing a grid for detection traps, field surveys, and monitoring. Climate change implications for biosecurity are also important with the shifting of pest ranges. Our study contributes to raising the awareness of the potential distribution of TPP and CLSo and thereby may assist regulatory agencies in prioritising actions that may minimise the possible threat of TPP to global agriculture.