Stability Constrains How Populations Spread Risk in a Model of Food Exchange

Food exchange between human populations can mitigate the risk arising from variable food production. Networks of exchange vary according to context but tend to fall into a relatively small number of qualitatively different types, including altruism, reciprocity, and resource pooling. This apparent canalization raises the question of whether specific networks of food exchange exhibit features that allow them to persist in the longer term, and we address this question by using a model of food exchange among multiple populations. First, we show that essentially any mode of exchange in our model will help to buffer the risk associated with local environmental variability. However, we also find that only a limited set of networks will guarantee population stability when resources are scarce. These stabilizing networks overlap empirical classifications of exchange, suggesting that population stability could provide an important filter for viable modes of exchange.