Archaeology of the Moundville Chiefdom: Chronology, Content, Contest

6. Human Subsistence at Moundville: The Stable-Isotope Data

6. Human Subsistence at Moundville: The Stable-Isotope Data MARGARET J. SCHOENINGER AND MARK R. SCHURR STABLE CARBON AND NITROGEN ISOTOPE analyses of approximately 250 human, animal, and maize samples indicate changes in human subsistence strategies during occupation at pre-Contact Moundville in Alabama. Data suggest increased maize use between Moundville I and the subsequent Moundville II phase. Most important, a decrease in bI3C values between Moundville III and the subsequent Moundville IV phase (t =2,96, df := 53, significant at the 0.01 level, two-tailed test) coupled with a lack of change in 515 N values suggests a decrease in dependence on maize and an increased dependence on gathered plant foods. This supports earlier hypotheses explaining Moundville's collapse as due to internal rather than external factors. As befits a site studied as intensively as Moundville (Peebles et al. 1982), the diet ofits inhabitants deserves attention. This project was developed toward that end with several questions in mind. First, what was the pattern of change in human diet over time at Moundville? Was there a difference between the earliest period of settlement (Moundville I) and later periods (Moundville II and III)? Was there a difference between the periods ofMoundville's greatest florescence (Moundville II and III) and the last period (Moundville IV, previously called Alabama River phase), during which Moundville's control of the polity along the Black Warrior River seems to have been lost (Peebles 1987b). Second, what 120 Human Subsistence at lVloundville 12 I was the pattern of human diet among status clusters previously identified by Peebles (Peebles I974)? Did individuals of higher status have diets that differed from those identified by mortuary analysis as lower status? Third, were there any differences in diet between males and females at Moundville? Fourth, once the pattern of diet at the site is established, does it provide any information about Moundville's loss of political control? The method used is analysis ofcarbon- and nitrogen-stable-isotope ratios in bone collagen to detect diets of individuals from different time periods, different status positions, and different sex. In general, the present study is complementary to the analyses of the floral (Scarry 1986) and faunal (Michals 1981) remains from Moundville. Such midden analyses are imperative for identifying diet items and indicating subsistence trends over time, but it is not usually possible to detect individual differences in diet from such studies. The attention paid to Moundville's middens since the I970S, however, has permitted an assessment of relative importance of diet items at different periods that has been impossible at most sites. Together, the midden and stable-isotope studies should result in a more accurate reconstruction of diet in the prehistoric Moundville community. For carbon, the stable-isotope ratios (l3C/I2C), represented as DI3 C values in per mil (%0) notation, in bone collagen reflect the 13e/12c ratio in the diet of the individual (DeNiro and Epstein 1978). The utility of this method is based on an average 1 percent (10 per mil) difference in stable carbon isotope ratios between plants that synthesize a three-carbon molecule during the first phase of photosynthesis (referred to as C3 plants) and other plants (referred to as C4 plants), such as tropical grasses (e.g., maize) that synthesize a four-carbon molecule in the first phase (O'Leary 1988). The difference in plant ratios is reflected in the tissues of animals, including humans, that eat them. Humans or animals such as the white-tailed deer that eat C 3 plants have tissues with a C3 signature, because their tissues reflect the 8l3 C values of the C3 plants they consume. Similarly, humans who eat C4 plants or animals that eat C4 plants, such as bison on the Great Plains, have tissues with a C4 signature. The majority ofwild North American plants of the southeastern United States are C3, and maize is the only major C4 plant that was an important dietary component prehistorically in the Moundville area. For this reason, human bone collagen D13 C values with a C4 signature indicate a diet including maize or animals that ate maize. 122 SCHOENINGER AND SCHURR Stable nitrogen isotope ratios (lSN/14N) in bone collagen, presented as b15 N values in per mil notation, also reflect the values in the individual 's diet (DeNiro and Epstein 1981). Among terrestrial plants (see Delwiche et al. 1979; Virginia and Delwiche 1982), those that fix atmospheric nitrogen (such...