When to defend? Optimal territoriality across the Numic homeland
Ashley K Parker, Christopher H Parker, Brian F Codding
Explanations for the complex human decisions that lead to territoriality have focused on models of economic defendability. While powerful, these models fail to explain variation in territorial behavior in all cases. To help overcome this limitation, here we offer an approach that synthesizes the logic of economic defendability with a general optimality model from behavioral ecology: the marginal value theorem (MVT). Through the MVT we add considerations of how resource profitability, in addition to abundance, alters the amount of time individuals should spend foraging in order to meet caloric requirements, and how far they should travel between foraging locations. Where and when individuals rely on abundant, but lower profitability resources, they should spend more time foraging and less time traveling, which leads to smaller territories that are easier to defend, and wherein each unit of land has a greater economic value per capita thereby increasing the benefits of economic boundary defense. Numic foragers of the Great Basin and surrounding areas provide an illustrative case study to validate this general ecological model. The results show that individuals exploiting high density but low profitability resources live in smaller territories and have higher rates of resource privatization, thereby explaining societal differences between Northern Paiute and Shoshone bands. Importantly, because defended resource patches are the target of women's foraging, the payoffs to territoriality are likely structured by women's risk averse foraging decisions. We suggest this model is capable of explaining variation in hunter-gatherer territoriality worldwide.