Abstract
An extensive ecological literature applies stable isotope mixing models to derive quantitative dietary reconstructions from isotope ratios of consumer tissues. While this approach works well for some organisms, it is challenging for consumers with complex, varied diets, including humans; indeed, many archaeologists have avoided the use of mixing models because uncertainties in model outputs are sufficiently large that the findings are not helpful in understanding ancient lifeways. Here, we exploit an unparalleled opportunity to evaluate the feasibility of dietary quantification in a nutritionally and isotopically complex context on the Cape Peninsula, South Africa. Delta values (δ13C and δ15N) of 213 indigenous food samples enable us to characterise four food groups: terrestrial plants, terrestrial vertebrates, marine invertebrates and marine vertebrates. A recent study of baboons that consumed marine and terrestrial foods provides insight into the relationship between such foods and consumer tissue isotopes. We use this information to refine our interpretation of δ15N and especially δ13C in bone collagen from 35 archaeological hunter-gatherers, achieving better estimates of the relative importance of marine and terrestrial foods in the diet than has hitherto been possible. Based on Bayesian stable isotope mixing model (SIMM) outputs, we infer that the trophic enrichment factor (TEF) for δ13Cbone collagen in these coastal humans is closer to +3 than +5‰. In the most 13C- and 15N-rich individuals, 65–98% of bone collagen (95% credible intervals) derived from marine foods. Conversely, in 13C and 15N-poor individuals, 7–44% of bone collagen derived from marine foods. The uncertainties discussed here highlight the need for caution when implementing SIMMs in studies of consumers with complex diets. To our knowledge, this work constitutes the most detailed and most tightly constrained study of this problem to date.
Highlights
Δ13C values ranged from −26.5‰ to −7.7‰ and δ15N values from −5.1‰ to 19.4‰ (Fig 2)
There were significant between-group differences in δ13C (χ23 = 127.71, p < 0.001) and δ15N values (χ23 = 162.92, p < 0.001), with all food groups differing from all other groups in both cases (Table 1)
Both marine food groups exhibited higher δ15N values than terrestrial groups, but the marine–terrestrial disparity in δ15N values was less pronounced than that in δ13C values. Results of these statistical tests suggest that these groups are appropriate for use in isotopebased models of archaeological humans from the Cape Peninsula
Summary
Since stable isotope measurements of consumer tissues were first used as a tool for dietary reconstruction in the late 1970s [1,2,3], researchers have sought to use this approach to quantify. Ancient coastal human diets from Bayesian stable isotope mixing models and a primate analogue. Service (https://www.daad.de/en/) and University of Cape Town. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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