Predicting the impact of climate change on the invasive decapods of the Iberian inland waters: an assessment of reliability

In an effort to predict the impact of climate change on the distribution of existing invasive species, niche-based models (NBMs) are being increasingly used to make forecasts. Here, we investigate the reliability of these models in predicting future climatic suitability for 4 invasive decapods of the Iberian Peninsula: Cherax destructor, Eriocheir sinensis, Pacifastacus leniusculus and Procambarus clarkii. From an ensemble of forecasts generated by 5 distinct algorithms (generalized linear models, artificial neural networks, support vector machines, random forests and alternating decision trees), we calculated consensus predictions for current conditions and 3 future time periods (2030, 2050 and 2080) under low and high scenarios of greenhouse gas emissions. Three criteria were examined to infer the robustness of the forecasts: ability to predict current distributions, inter-model variability and degree of environmental extrapolation. Our results indicate an overall decline in climatic suitability for the 4 invaders as time progresses. However, we also identified highly distinct levels of predictive uncertainty among species. Good indicators of reliability were found for Procambarus clarkii and Pacifastacus leniusculus, whereas the predictions for C. destructor showed low predictive performance, low inter-model agreement and wide areas of environmental extrapolation. For E. sinensis, the models also showed high variability with respect to areas projected to lose climatic suitability. Overall, our results highlight the need to consider and evaluate multiple sources of uncertainty when using NBM predictions for invaders under current and future conditions.