Distribution modelling and conservation assessment for helmeted terrapins (Pelomedusa spp.)

For decades, the genus Pelomedusa has been thought of as containing only a single species that is widely distributed in sub-Saharan Africa, the Arabian Peninsula, and Madagascar. However, ten species and up to five candidate species have been recognized recently. For these taxa, ecological information is scarce and distribution ranges are often only incompletely known. In this study, ecological niche spaces were estimated for eight Pelomedusa species, using a maximum entropy algorithm and geographical, climatic, and topographic information. Using the obtained models and Schoener’s D and Hellinger’s I indices, areas of sympatry between species were estimated and candidate areas for possibly overlooked taxa were identified. Furthermore, differences in niche spaces between species were assessed. The ecological niche models revealed geographical spaces that match the predicted niche of the eight examined species. However, for P. subrufa sensu stricto, the distribution range of the introduced populations in Madagascar was not predicted. Our models, together with statistical analyses, indicate that the studied Pelomedusa species occupy different geographical spaces. Areas of sympatry with significant niche overlap were identified between some species pairs. Yet, Pelomedusa species are generally allopatrically or parapatrically distributed. A minimum of five candidate regions possibly harbouring unknown taxa were identified. Our results provide a better understanding of the distribution ranges of Pelomedusa species and, thus, can serve as a basis for conservation planning.