Decision Making in Subsistence Herding of Sheep and Goats in the Middle East.
Redding, Richard William, Jr.
1981
Abstract
Variation in the sheep/goat ratio, age structure, and sex ratio among reproductives has been observed in extant flocks of Middle Eastern sheep and goats, and in archaeological faunal samples of sheep and goat remains from the Middle East. The state of each of these parameters in a flock reflects decisions made by the human herders. Such decisions are based on differences between sheep and goats in ecological, physiological, behavioral, reproductive, and production characteristics, and the goal of the human herders. Evolutionary ecologists have developed a group of models, based on optimization theory, for examining decision making in subsistence behavior among predators. An optimal foraging approach has been used in this study to examine decision making in structuring flocks of sheep and goats for subsistence herding in the Middle East. Ecologists utilizing optimal foraging models usually assume that the goal of the predator is maximization of energy intake and the hypothesis being tested is that the predator is behaving in an optimal fashion. In this study it was assumed that herders optimize and sets of implications for three alternative goals, maximization of energy offtake, maximization of protein offtake, and herd security, were derived from the models and compared with archaeological faunal data. As an initial step in constructing the models the literature on the ecology, physiology, behavior, reproduction, and production in Middle Eastern sheep and goats was reviewed. Growth curves for a herd of 100 ewes and a herd of 100 does were produced, and the stable age distributions expected for each herd were determined. The number of milking ewes/does and the expected offtake of animals, lambs/kids and adult females, were determined from the stable age distributions. These data were used to calculate expected annual yields of calories and nutrients from meat and milk for sheep and goats. A budget curve, representing flocks of equal cost to the human herders, were constructed for modeling the sheep/goat ratio and adult sex ratio. The data on the characteristics of sheep and goats were used to construct indifference curves or each of the goals. These indifference curves were fitted to the budget curves and expected solutions for each goal were determined. No difference between the solutions for the goals of maximization of energy offtake and maximization of protein offtake were found. This suggests that herders optimizing for one of these goals, optimizes for both. The age structure of flocks of sheep and goats was not modeled graphically; instead, expected survivorship curves for each of the goals were derived from hypothetical schedules of slaughter congruent with each of the goals, and estimates of animals available for consumption based on the stable age distributions. A comparison was undertaken of the implications for each of the goals, for each herd parameter, with faunal data from the archaeological sites of Tappeh Sarafabad, Tepe Farukhabad, Ali Kosh, Tepe Siahbid, and Tepe Dehsavar. The sheep/goat ratios for these sites, when based on reasonable sample sizes, supported a conclusion that the goal of the human herders was herd security. The age structure data from the sites, in the form of survivorship curves, proved less conclusive, but also suggested that the goal was herd security. The observed sheep/goat ratios, adult sex ratios, and age structure data, in the form of age of slaughter of adult females, among extant herders were examined, but the implications derived for the goals were not rigorously tested. The ethnographic data from human groups not extensively involved in production for a market, suggested that extant herders are structuring their flocks to maximize herd security.Types
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