Alien turtles in Spain: Modeling a growing problem

Abstract

Four native chelonians species occur in Spain, three of which are severely threatened. In recent surveys, 25 species of alien turtles and tortoises were reported, some of which had established breeding populations and interfered with native species. In this study, we used ecological niche models to evaluate which regions are more vulnerable to colonization by alien turtles and tortoises and which alien chelonians show substantial environmental overlap with native species. The parameters of the ecological niche models were iteratively optimized using Akaike procedures, and we assessed the projection transferability between donor and recipient geographic regions using Mobility-Oriented Parity estimation. Our results indicated that the Mediterranean and some Atlantic rivers (Miño-Sil and Guadalquivir) are particularly vulnerable to colonization by semi-aquatic alien turtles, while southwestern Spain is exposed to colonization by alien tortoises. The aquatic species most susceptible to overlap with the four species of native turtles are those native to the cold and warm temperate regions of North America and China: Apalone spinifera, Chelydra serpentina, Chrysemys picta, Mauremys mutica, Mauremys reevesii, Mauremys sinensis, Pelodiscus sinensis, Sternotherus odoratus, and Trachemys scripta. These results highlight the importance of establishing stricter trade regulations for certain species with a focus on protecting vulnerable areas.