Invasive terrapin species have a major impact on freshwater ecosystems, threatening the endangered species Emys orbicularis. In addition to the widely introduced Mauremys leprosa and Trachemys scripta, new exotic species from the genus Graptemys and Sternotherus are being released in the environment. Furthermore, basins where native and exotic terrapins co-occur have been invaded by the Asian clam Corbicula fluminea. In this work we investigated diet breadth and degree of trophic overlap for one native and four exotic species. Additionally, we aimed to explore the potential of native and exotic terrapins to feed upon C. fluminea. Comparisons among two known E. orbicularis populations were performed to determine if long term co-occurrence with C. fluminea leads to an adaptive feeding behaviour. Our results suggest diet overlap and strong kinematic differences among native and exotic terrapins, with greater feeding capabilities and a competitive advantage for the exotic species. In this regard, the opportunistic behaviour of exotic species contrasts with the adaptive pattern of the native species. Based on our findings, we speculate about three plausible terrapin responses to C. fluminea invasion.

Financial support (to N. F-R.) came from a pre-doctoral fellowship from the autonomous government of Galicia (Xunta de Galicia Plan I2C, PRE/2013/400).