Return Rates For Tropical Lowland Resources

The adoption of maize and the development of maize-based food production in the Soconusco region resulted from a series of individual decisions regarding diet choice made by people over several millennia. These choices were made in specific socioecological settings that resulted from changing environmental conditions, both natural and human induced, and fluctuating social landscapes impinging on the availability of resources, especially territoriality and increases in social complexity. Optimal foraging theory (OFT) predicts that foragers will economize with respect to dietary choice, selecting resources, or patches, that maximize the rate of energy gained per unit energy expended in locating, catching/ collecting, and processing prey. Dietary choice is therefore constrained by the availability of resources and social factors limiting access to them such as food taboos or territoriality. Given these environmental and social constraints, the most efficient food acquisition strategies available, it is argued, would be favored by natural selection because extra resources, or time saved, can be invested in additional offspring or provisioning existing offspring or mates. Nutrition and overall health have also been directly correlated with fertility and child mortality rates in different societies (Butz and Habicht 1976; Hill et al. 1987; Moseley and Chen 1984).

Ranking wild resources from highest to lowest returns helps determine the most likely dietary mix in a region and can be used to predict changes in diet breadth when ecological conditions change (e.g., depressed availability of higher ranked resources; Cannon 2003). Whether or not a new cultigen is incorporated into the dietary regime of a forager should be related to the availability of highly ranked wild resources and overall diet breadth (Winterhalder and Goland 1997). Ethnographic studies support the notion that caloric returns, rather than food preference, are robust predictors of diet choice (Hill et al. 1987; Winterhalder and Smith 2000). These studies also show that the size of a resource alone is not a good predictor of these dietary rankings, because resource value results from the caloric value of the resource minus the costs of acquisition and processing. Estimating return rates in prehistoric settings is challenging because each estimation depends upon encounter rates, procurement/processing techniques, and transportation costs, all of which are not directly knowable from the archaeological record. The costs and benefits of exploiting certain types of resources must be inferred from ethnographic studies within similar ecological contexts where this kind of economic data is collected and quantified, and/or from experimental studies that estimate resource return rates for labor investment in producing various technologies.

We examine two ethnographic studies from other tropical forest settings in the New World to garner the economic data needed to estimate return rates for different resources since firsthand observations of foraging practices in the Soconusco region are not available because traditional systems of agriculture and food extraction have given way to larger-scale ranching and cash-crop agriculture. One of these studies was conducted by James Nations and Robert Nigh (1980) among the Lacandon Maya, a small-scale farming/foraging population that re-colonized a portion of the southern Maya lowlands (Chiapas, Mexico) several centuries ago. Re-colonization of this region followed a long period of tropical forest regeneration that ensued with the collapse and abandonment of this area by the Classic Period Maya (AD 250-900; Webster 2002). We consider the foraging practices of these people to provide an apt analogy to the strategies practiced by early foraging and farming populations in the Soconusco region. Unfortunately, detailed information regarding the return rates of different plants and animals were not recorded in this study. To remedy this situation we turn to a second study conducted among Ache foragers who occupy a section of tropical forest in the Amazon and where a detailed study of return rates on a similar suite of resources has been conducted (Hill et al. 1987). We recognize that these data are not ideal, but we argue that they provide at least an approximation of dietary rankings in the forested coastal plain and piedmont zones within the Soconusco region. Ultimately, we are interested in comparing return rates of locally available wild resources with estimated rates of return for maize agriculture at various points in the past (see Tables 6.4 and 6.5 for estimated rates of return for maize-based food production).

The Lacandon Maya practice a diverse land-use system that capitalizes on different resource types from the primary and secondary forest and a variety of aquatic habitats; marshes, rivers, lakes, and streams (Nations and Nigh 1980, 8). At the heart of the Lacandon system is a form of slash-and-burn, or swidden, agriculture, where

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