Trophic niche partitioning among three sympatric anuran species in a South Korean forest ecosystem based on stable isotope analysis

Stable isotope analysis (SIA) is a powerful tool for assessing resource use and trophic structure, enhancing understanding of coexistence mechanisms among sympatric species. In this study, we analyzed carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes in bone collagen of three coexisting anuran species-Bombina orientalis, Rana uenoi, and R. huanrenensis-from South Korean forest to evaluate their isotopic niches, resource partitioning, and within-population variation. Rana uenoi and R. huanrenensis utilized a broad range of resources with high overlap, suggesting they likely share dietary habits and occupy similar trophic roles. In contrast, relative δ¹⁵N enrichment of B. orientalis indicates a distinct trophic niche, although its resource utilization was not entirely segregated from that of the two Rana species. Furthermore, large groups of both Rana species tended to exploit a wider variety of resources than smaller ones, whereas B. orientalis showed no isotopic sex differences. All three species displayed ontogenetic niche shifts, with B. orientalis increasingly relying on aquatic-origin resources, while the two Rana species shifting toward terrestrial-origin resources. These findings provide insight into the trophic dynamics of forest-dwelling anurans and may serve as a baseline for ecological and conservation research in the future.