Morphology, Performance, and Ecology of Three Sympatric Turtles in a Tropical Dry Forest

Resource partitioning in communities is often achieved by sympatric species having different morphologies that allow them to access different resources. This is because differences in morphology influence an organism's capability to perform a task that is relevant to their ecology. Here, we compare limb, shell, and head morphology, swimming performance, habitat use, and diet of three species (Rhinoclemmys rubida, R. pulcherrima, and Kinosternon chimalhuaca) that co-occur in the tropical dry forest of Chamela, Jalisco, Mexico. We found that these species do not overlap in both habitat or diet, and the overlap that we observed in habitat was contrasted by differences in diet. We also found a consistent relationship among limb and shell morphology, swimming speed, and habitat. Rhinoclemmys rubida occupies the driest deciduous forest atop and along hills, has shorter hands, less interdigital webbing, longer plastrons, more-domed shells, and slower swimming speeds in proportion to body size. In contrast, Kinosternon chimalhuaca exclusively occupies arroyos or seasonal streams, has longer hands, more interdigital webbing, smaller plastrons, less-domed shells, and faster swimming speeds in proportion to its body size. Rhinoclemmys pulcherrima was found in all habitats and intermediate in morphology and swimming speed between the other two species. Therefore, in this study system, limb and shell morphology are good indicators of habitat differences between turtle species. These differences are likely due to the influence that limb and shell morphology have on swimming performance. Relationships between head morphology and diet were less clear, which might be the result of changes in behavior or habitat rather than morphology. Patterns of resource partitioning in Chamela seem to coincide with other studies of turtle communities, which suggests that relationships among morphology, performance, and ecology that we observe here might be a general pattern across turtles.