Interspecific differences in heat exchange rates may affect competition between introduced and native freshwater turtles

Abstract

In the Iberian Peninsula, the red-eared slider (Trachemys scripta elegans) is an introduced invasive species that is displacing the endangered native Spanish terrapin (Mauremys leprosa). However, the nature of competitive interactions is relatively unclear. In temperate zones, mechanisms for maximizing heat retention could be selectively advantageous for aquatic turtle species, since individuals usually lose the heat gained from basking very rapidly when entering the water. We hypothesized that interspecific differences in morphology, and thus, in heating and cooling rates, might confer competitive advantages to introduced T. scripta. We compared the surface-to-volume ratios of both, introduced and native turtles, basing on biometric measures, and their effects on thermal exchange rates. T. scripta showed a more rounded shape, a lower surface-to-volume ratio and a greater thermal inertia, what facilitates body heat retention and favors the performance of activities and physiological functions such as foraging or digestion, thus aggravating the competition process with native turtles in Mediterranean habitats. [PUBLICATION ABSTRACT]