Isotopic niche in the eastern long-necked turtle, Chelodina longicollis (Testudines: Chelidae), along a natural-urban gradient in southeastern Australia

Urbanisation is one of the most common threats to many native species, while others are capable of taking advantage of urban areas and even expanding their niche in urban-natural systems. The analysis of stable isotopes of carbon and nitrogen in a tissue sample provides data that can elucidate food web dynamics and trophic ecology of an animal. Our study aimed to evaluate variation in food resource exploitation in the freshwater turtle Chelodina longicollis along a habitat gradient (natural, rural, and suburban areas), and intraspecific niche variation among demographic groups (juvenile, adult male, adult female). We found that isotopic composition of C. longicollis varied along the habitat gradient, with δ15N levels highest in suburban environments, intermediate in rural areas, and lowest in the nature reserve. δ13C values were higher in suburb and rural turtles compared to those on the nature reserve. Besides some intraspecific differences in δ13C as evidence of demographic partitioning of the foraging niche, demographic groups apparently feed on the same trophic level within habitats. Our study included samples from small juveniles (<10 cm) and helped to cover a gap of understanding in intraspecific niche for C. longicollis. Future research should evaluate the reasons turtles in suburban areas are enriched in δ 15N, either because they are foraging on different trophic levels or because they are feeding on prey enriched in nitrogen.