• Diet‐tissue stable isotope (Δ 13C and Δ 15N) discrimination factors for multiple tissues from terrestrial reptiles

      Steinitz Ronnie; Lemm, Jeffrey M.; Pasachnik, Stesha A.; Kurle, Carolyn M. (2015)
      Rationale Stable isotope analysis is a powerful tool for reconstructing trophic interactions to better understand drivers of community ecology. Taxon?specific stable isotope discrimination factors contribute to the best use of this tool. We determined the first ?13C and ?15N values for Rock Iguanas (Cyclura spp.) to better understand isotopic fractionation and estimate wild reptile foraging ecology. Methods The ?13C and ?15N values between diet and skin, blood, and scat were determined from juvenile and adult iguanas held for 1 year on a known diet. We measured relationships between iguana discrimination factors and size/age and quantified effects of lipid extraction and acid treatment on stable isotope values from iguana tissues. Isotopic and elemental compositions were determined by Dumas combustion using an elemental analyzer coupled to an isotope ratio mass spectrometer using standards of known composition. Results The ?13C and ?15N values ranged from ?2.5 to +6.5? and +2.2 to +7.5?, respectively, with some differences among tissues and between juveniles and adults. The ?13C values from blood and skin differed among species, but not the ?15N values. The ?13C values from blood and skin and ?15N values from blood were positively correlated with size/age. The ?13C values from scat were negatively correlated with size (not age). Treatment with HCl (scat) and lipid extraction (skin) did not affect the isotope values. Conclusions These results should aid in the understanding of processes driving stable carbon and nitrogen isotope discrimination factors in reptiles. We provide estimates of ?13C and ?15N values and linear relationships between iguana size/age and discrimination factors for the best interpretation of wild reptile foraging ecology. Copyright ? 2015 John Wiley & Sons, Ltd.