Interference competition between native Iberian turtles and the exotic <em>Trachemys scripta</em>

Abstract

The red-eared slider, Trachemys scripta elegans, is a worldwide invasive species, currently introduced in most freshwater habitats as a consequence of the exotic pet trade. In the Iberian Peninsula, this American turtle is competing and displacing the Iberian turtles, Emys orbicularis and Mauremys leprosa. Recent studies have pointed out to diverse competitive advantages of sliders over Iberian terrapins. For instance, native turtles avoid chemical cues from T. scripta, which is more aggressive and dominant in direct competition for food and basking places. This avoidance behaviour displayed by Iberian terrapins might serve as a spacing mechanism to avoid unfavourable competitive interactions with the introduced species. Sliders also benefit from morphological and thermoregulatory advantages: they are more spherical, thus presenting a less surface to volume ratio and a greater thermal inertia that facilitates heat retention. On the other hand, introduced turtles show a more accurate assessment of predatory risk in altered habitats, and are more efficient predators of local prey than native species. These inter-specific asymmetries could contribute jointly to the greater competitive ability of introduced T. scripta, thus facilitating the expansion of this alien species in detriment of native populations of Iberian terrapins.