[C15] Evolution and Genetics & Interdisciplinary Studies

[C15-04] Diet breadth of foragers and coexistence of foragers and producers

*Yukiko Kawanishi¹, Yasuo Ihara¹ (1. The University of Tokyo (Japan))

Keywords:

hunter-gatherers,diet breadth model,population dynamics,relationships of foragers and food producers

Throughout most of their history, humans lived as foragers, relying on hunting, fishing, and gathering for food. During the Holocene, with the advent of farming, foragers in various parts of the world began to encounter food producers, which brought about changes on their lifeways. Some groups of foragers likely disappeared, perhaps being absorbed into farmer populations, and others may have switched their subsistence to be food producers themselves, while still others have persisted as foragers, coexisting with neighboring farmer or herder populations until today. It is notable that foragers do not immediately or inevitably go extinct upon contact with farmers, and why some, but not other foragers have persisted is not fully understood. Meanwhile, studies based on the optimal foraging theory have investigated foragers' adaptive modification of subsistence strategies as a response to environmental change. In particular, Winterhalder et al. (1988) incorporated a diet breadth model into analysis of population dynamics, as an attempt to connect foragers' decision making on the ethnographic timescale with forager population dynamics on the archaeological timescale. Here, by extending Winterhalder et al.'s conceptual framework, we explore possible consequences of a forager-producer encounter on the persistence of forager populations, with foragers' adaptive modification of foraging strategies being considered. To this end, we develop a mathematical model that tracks population dynamics of two types of resources (one is more valuable than the other), foragers, and producers. We first analyze a model without producers to specify the states where the forager and resource populations coexist at a stable equilibrium. We then introduce producers into the model to see how the foragers' demographic state and foraging strategy may be altered, given their adaptive decision making. For example, the simplest model, in which foragers and producers do not interact directly, shows that a contact with producers never causes foragers relying only on the more valuable of two existing resources to broaden the diet breadth. This study may be useful to specify theoretically plausible types of transition in foragers' lifeways caused by an encounter with producers, and conditions under which they may occur. It may also help us deepen our understanding about why some foragers coexist with farmers and herders even today, while many others have disappeared.