Stable isotope analysis reveals inter- and intraspecific trophic relationships of the endangered Central American river turtle in southern Mexico

Trophic ecology studies enhance our understanding of species relationships within communities and ecosystems, providing critical information for conservation programs targeting endangered species. The Central American river turtle (Dermatemys mawii) is one of the most critically endangered testudine species worldwide, yet its trophic ecology has been scarcely studied. Based on stable isotope analysis (delta 13C and delta 15N), we applied community-wide metrics and stable isotope mixing models to assess the intraspecific variation in the isotopic niche of D. mawii among different age and sex categories, its interspecific relationships with dominant fish species, and the relative contribution of basal resources to selected aquatic consumers in an oxbow lake in southern Mexico. The community-wide metrics suggested that D. mawii juveniles consumed a greater variety of food resources and/or had access to a wider variety of habitats than adults, regardless of sex. Through the mixing models we detected that the aquatic plant Pistia stratiotes was the main dietary source for adult females, while riparian plants were more important for juveniles and adult males, suggesting intraspecific niche partitioning. We also identified distinct energy pathways for D. mawii and fish, with turtles relying on vascular plants (both riparian and aquatic) while fish primarily depended on seston. Our findings suggest that D. mawii may play an important role in nutrient cycling and potentially regulate the presence of the free-floating macrophyte P. stratiotes at the study site.