Species Distribution Modeling Provides New Insights into Different Spatial Distribution Patterns among Native and Alien Freshwater Turtles in Japan

Abstract: The endemic Japanese freshwater turtle Mauremys japonica is the most common turtle in foothill areas, whereas it is usually absent or scarce in lowland environments in Japan. In contrast, another turtle, Reeves' pond turtle (M. reevesii), usually inhabits lowland areas. Explanation of this pattern based on habitat segregation between M. japonica and M. reevesii remains controversial because several studies have emphasized that M. reevesii is not indigenous but rather introduced from mainland China and the Korean Peninsula. The newly proposed hypothesis is that M. reevesii and the recently introduced red-eared slider (Trachemys scripta elegans) have excluded M. japonica from certain suitable habitats in lowland areas. In this study, to test whether M. japonica originally had a broad distribution range covering the habitats currently occupied exclusively by M. reevesii and T. s. elegans, we applied species distribution modeling using MaxEnt and ENMTools to estimate the suitable habitats and ecological niches of M. japonica, M. reevesii, and T. s. elegans, respectively, and examined these similarities. The models showed that M. japonica had the largest suitable habitat range, from flatlands to foothill areas, compared to that of alien species; however, almost the entire habitat area of the native turtle and that of the aliens overlapped. Moreover, these turtles possessed significantly high niche similarity. These results are consistent with the hypothesis that recent species interactions have shaped the distribution of indigenous and alien turtles, although the precise ecological and evolutionary processes have not yet been determined.