Between the hammer and the anvil: how the combined effect of global warming and the non-native common slider could threaten the European pond turtle

The European pond turtle Emys orbicularis is seriously threatened across Europe by the non-native common slider, Trachemys scripta, which is included among the 100 most invasive species worldwide. Using ensemble forecast techniques, we analysed the influence of climatic factors on the current distribution of these two species, subsequently projecting the obtained models under two Representative Concentration Pathways (RCPs) to 2050 and 2070, to investigate if global warming would boost direct competition within our study region. We implemented a gap analysis in GIS environment to assess how protected areas (PAs) may be affected by a loss of suitable area for E. orbicularis and by an expansion of T. scripta. An analysis of attitudinal range shift was evaluated, based on obtained projections. We found that both species may gain suitable area in the future, possibly because of the positive effect of increasing temperatures, and are predicted to shift from plain-to-hilly areas towards higher altitudes. These trends result in an increasing overlap of potentially suitable areas for both species, particularly within PAs; moreover, a niche analysis highlights that the results obtained are linked to the environmental niches of the two species. Our findings suggest the necessity, particularly for PAs' authorities, of field monitoring of T. scripta and further research to more comprehensively assess biotic and abiotic factors influencing the invasiveness of this species.