Zinc isotope ratios of bones and teeth as new dietary indicators: results from a modern food web (Koobi Fora, Kenya)

Abstract

In order to explore the possibilities of using zinc (Zn) stable isotope ratios as dietary indicators, we report here on the measurements of the ratio of stable isotopes of zinc ((66)Zn/(64)Zn, expressed here as δ(66)Zn) in bioapatite (bone and dental enamel) of animals from a modern food web in the Koobi Fora region of the Turkana Basin in Kenya. We demonstrate that δ(66)Zn values in both bone and enamel allow a clear distinction between carnivores and herbivores from this food web. Differences were also observed between browsers and grazers as well as between carnivores that consumed bone (i.e. hyenas) compared to those that largely consume flesh (i.e. lions). We conclude that Zn isotope ratio measurements of bone and teeth are a new and promising dietary indicator.

Figure 1. Sampling area in the Sibiloi National Park, Kenya.

The areas were defined by Brown and Feibel (1986). All animals come from the areas 101, 102 and 103 except for three from the dik diks (area 117) and three from the Lesser Kudus (Two from area 1A and one from an area located outside of the map). Blank map of Africa from Daniel Dalet (histgeo.ac-aix-marseille.fr). The map showing the sampling areas was created using Adobe Illustrator CS6.

Figure 2. δ⁶⁶Zn values in bones (plain symbols) and dental enamel (open symbols) grouped by species.

Plant values are also displayed. Error bars represent two SD.

Figure 3

Left: δ⁶⁶Zn range in plants as well as in bones (top, (A)) and in dental enamel (bottom, (B)) for each type of diet. The boxes represent the 25^th–75^th percentiles (with the median as a bold horizontal line) and the whiskers show the 10^th–90^th percentiles. Right: δ⁶⁶Zn vs δ⁶⁸Zn for plants and animal bones (top) and teeth (bottom) of the Koobi Fora trophic chain. As expected from mass-dependent isotope fractionation, the slopes of the least-squares straight line fit to the data are close to 2. Error bars correspond to two SD.

Figure 4. δ⁶⁶Zn bone and plant values for three African trophic chains: Koobi Fora, Kenya (this study), Kruger Park (South Africa) and Western Cape (South Africa).

Note that plant isotopic compositions vary between sites. Hyenas show higher δ⁶⁶Zn bone values than other carnivores. Error bars corresponds to one SD.