Technical Note: Calcium and carbon stable isotope ratios as paleodietary indicators
Amanda MelinBrooke E. CrowleyShaun T. BrownPatrick V. WheatleyGillian L. MoritzFred Tuh Yit YuHenry BernardDonald J. DePaoloAndrew D. JacobsonNathaniel J. Dominy
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ABSTRACT Calcium stable isotope ratios are hypothesized to vary as a function of trophic level. This premise raises the possibility of using calcium stable isotope ratios to study the dietary behaviors of fossil taxa and to test competing hypotheses on the adaptive origins of euprimates. To explore this concept, we measured the stable isotope composition of contemporary mammals in northern Borneo and northwestern Costa Rica, two communities with functional or phylogenetic relevance to primate origins. We found that bone collagen δ 13 C and δ 15 N values could differentiate trophic levels in each assemblage, a result that justifies the use of these systems to test the predicted inverse relationship between bioapatite δ 13 C and δ 44 Ca values. As expected, taxonomic carnivores (felids) showed a combination of high δ 13 C and low δ 44 Ca values; however, the δ 44 Ca values of other faunivores were indistinguishable from those of primary consumers. We suggest that the trophic insensitivity of most bioapatite δ 44 Ca values is attributable to the negligible calcium content of arthropod prey. Although the present results are inconclusive, the tandem analysis of δ 44 Ca and δ 13 C values in fossils continues to hold promise for informing paleodietary studies and we highlight this potential by drawing attention to the stable isotope composition of the Early Eocene primate Cantius . Am J Phys Anthropol 154:633–643, 2014. © 2014 Wiley Periodicals, Inc.Keywords:
Isotope Analysis
Mammal
Stable isotope analysis provides an integrated measure of diet source and trophic position and is becoming an increasingly popular tool in studies of food web structure and function. However, stable isotope analysis can require sacrificing whole organisms, which is not always practical or ethical. As an alternative, biopsy punches cause minimal mortality in fish and provide enough sample for stable isotope analysis. Researchers commonly use smaller tissue samples for stable isotope analysis. Such analyses rely on the untested assumption that the stable isotope ratios from small tissue samples are representative of whole organism stable isotope ratios. Here we test this assumption by comparing stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) from tissue plugs and whole organisms over a range of fish sizes. We show that plugs from fish smaller than approximately 90 mm total length introduce a positive bias in δ 15 N. For larger fish, plugs provide a reliable and accurate means of measuring δ 15 N and δ 13 C, with the caveat that they introduce some variability in δ 13 C. Inclusion of overlying skin did not affect stable isotope measurements in our tissue samples.
Isotope Analysis
Isotopes of nitrogen
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δ15N
Isotopes of nitrogen
Isotope Analysis
Isotope-ratio mass spectrometry
Omnivore
Isotopic signature
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