Spread risk assessment of invasive axis deer using bioclimatic niche models

Abstract

Ecological niche models are useful tools for predicting and managing biological invasions. However, their reliable implementation and derived applications could be biased by niche shifts among native and invaded areas and by non-equilibrium dynamics. We calculated bioclimatic niche overlap between native and invaded ranges, and tuned species distribution models trained on both the native range (native model), and the native and invasive ranges (complete model) for the axis deer (Axis axis) to assess its invasion risk potential worldwide. Our results suggest that the axis deer shifted its realized niche in some invaded areas where most of the climatic niche available was contained within the environmental conditions from the native range. We found signals of non-equilibrium dynamics between native and invaded niches due to several unfilled areas in invaded regions. The native and complete models are similar in their projection for the equatorial region but differ significantly in the tropical regions. The first fails to predict areas where the species was successfully established. This difference reinforces the idea of using all the occurrences for predicting possible invaded areas, and that invasive species can somehow shift their niche. The complete model predicted that the most climatically suitable regions for the species worldwide were in tropical and subtropical climates, particularly the Neotropics and Afrotropics. While the species has been already established in the Neotropics, it hasn’t in the latter. Therefore, our work emphasized the importance of a nuanced understanding of the potential distribution of invasive species to inform more effective management measures.