Ancient Borinquen: Archaeology and Ethnohistory of Native Puerto Rico

5. Ceramic-Age Dietary Patterns in Puerto Rico: Stable Isotopes and Island Biogeography

5 Ceramic-Age Dietary Patterns in Puerto Rico Stable Isotopes and Island Biogeography Anne V. Stokes Diet and foodways are among the most fascinating and important aspects of culture. A de¤ning attribute distinguishing cultural groups is based in large part on food habits. Archaeologists seek multiple lines of evidence to identify foods consumed by ancient peoples. These include animal and plant remains, artifacts, settlement patterns, and such distinctive features of the landscape as the remains of ditches, dikes, raised beds, and enriched soils. Each of these topics can provide substantial information on foods, although none by itself can tell the entire dietary story. Over the past two decades or so, stable isotope analysis has emerged as an important line of evidence in reconstructing past diets. Like other ¤elds of inquiry, stable isotope analysis does not have all the answers. What it uniquely offers, however, is an estimate of the isotopic composition of carbon and nitrogen in the overall diet. This estimate can then be evaluated independently by identifying bones, plant remains, artifacts, and such. Here I will evaluate the stable isotopes of carbon and nitrogen in human bones recovered from Maisabel and Paso del Indio, two large ceramic-age sites in Puerto Rico (Siegel 1989a, 1992; Siegel et al., this volume; Walker, this volume). I will interpret the results in terms of the isotopic compositions of potential plant and animal foods. Further, the results will be interpreted in the cultural contexts of the sites, locally within Puerto Rico and regionally across the West Indies. The interisland perspective will bene¤t from principles derived from island biogeography, a ¤tting way to look at peoples whose cultural ties spanned numerous islands in the Caribbean. The Process Stable isotope analysis allows us to measure the relative contribution of food groups to diet. This is possible because animals incorporate the stable isotopes of carbon (C) and nitrogen (N) into their bodies in different relative amounts that re®ect the isotopic compositions of their foods. By analyzing the bone collagen and apatite carbonate, a picture of prehistoric diet emerges. Isotopic ratios are expressed in the delta (δ) notation in parts per thousand (per mil or ‰) relative to a standard using the following equations: (13 C/12 C)sample – (13 C/12 C)PDB X 1000‰ δ13 C = (13 C/12 C)PDB (15 N/14 N)sample – (15 N/14 N)AIR X 1000‰ δ15 N = (15 N/14 N)AIR The standard used for carbon is Belemnitella americana, a marine fossil from the Peedee Formation in South Carolina (Craig 1957). The standard contains more 13 C than all dietary items and most human tissues, and therefore the δ13 C values will almost always be expressed as a negative number (Ambrose 1993; DeNiro and Epstein 1978). The standard measure for nitrogen isotope values is atmospheric nitrogen (AIR) (Mariotti 1983). Since most food resources and human tissues have more 15 N than the standard, the values normally are reported as positive numbers (Ambrose 1993; DeNiro and Epstein 1981). Certain food groups differ predictably in their carbon and nitrogen stable isotope values depending on their sources of carbon and nitrogen and their position in the food web (Figure 5.1). Most plants use a Calvin photosynthetic pathway, which produces a 3-carbon molecule, and are thus referred to as C3 plants. C3 plants include tubers (such as manioc), fruits, and temperate grasses. A second pathway, more common in hot or arid environments, results in a 4-carbon molecule (Hatch and Slack 1966; Hatch et al. 1967). C4 plants include tropical grasses such as Zea mays (corn), Seteria sp. (foxtail grass, rabo de zorra), and some amaranths and chenopods. Some xerophytic succulents and epiphytic plants, such as species of Agavaceae and Bromeliadaceae, use a third photosynthetic pathway, Crassulacean Acid Metabolism (CAM) (Bender 1968; O’Leary 1981; Smith et al. 1979; Troughton et al. 1974). The three pathways vary in how much 13 C they ¤x from atmospheric CO2, resulting in a separation between the δ13 C values of C3 and C4 plants with some overlap in [ ] [ ] 186 / Anne V. Stokes CAM values. In general, C3 plants range from −23 to −30‰ and C4 plants range from −8 to − 50‰) as to be out of the realm of possibility for human samples. Van Klinken blames some of the δ15 N values on contamination from soil humates (van Klinken 1991:96). Through proper extraction of the collagen with...