ISOTOPES IN BONES AND TEETH

Lipid normalization and stable isotope discrimination in Pacific walrus tissues

Analysis of stable carbon and nitrogen isotope values (δ¹³C and δ¹⁵N) of animal tissues can provide important information about diet, physiology, and movements. Interpretation of δ¹³C and δ¹⁵N values, however, is influenced by factors such as sample lipid content, tissue-specific isotope discrimination, and tissue turnover rates, which are typically species- and tissue-specific. In this study, we generated lipid normalization models for δ¹³C and investigated the effects of chemical lipid extractions on δ¹³C and δ¹⁵N in Pacific walrus (Odobenus rosmarus divergens) muscle, liver, and skin. We also evaluated tissue-specific isotope discrimination in walrus muscle, liver, skin, and bone collagen. Mean δ¹³C_lipid-free of skin and bone collagen were similar, as were mean δ¹⁵N of muscle and liver. All other tissues differed significantly for both isotopes. Differences in δ¹³C_lipid-free and δ¹⁵N among tissues agreed with published estimates of marine mammal tissue-specific isotope discrimination factors, with the exception of skin. The results of this work will allow researchers to gain a clearer understanding of walrus diet and the structure of Arctic food webs, while also making it possible to directly compare the results of contemporary walrus isotope research with those of historic and paleoecological studies.

Predicting diet, trophic level and palaeoecology from bone stable isotope analysis: a comparative study of five red deer populations

C and N stable isotope ratios of red deer (Cervus elaphus) bone collagen (154 individuals) from five modern populations occupying geographically different habitats are reported. No significant difference was observed between deer occupying forested and non-forested environments subject to similar climatic conditions suggesting a simple "canopy effect" is not observed. Mean population delta13C is negatively correlated with temperature whereas mean population delta15N is positively correlated with temperature. A weak but significant positive correlation was observed between deer age and collagen delta13C values from the Isle of Rum population (Scotland). The amount of intra-population isotope variability is not consistent among populations; thus significant numbers of individuals from each species are required for modern food web studies, for palaeodietary baseline data, and for palaeoecological studies.