Hunter-gatherer residential mobility and the marginal value of rainforest patches

Abstract

The residential mobility patterns of modern hunter-gatherers broadly reflect local resource availability, but the proximate ecological and social forces that determine the timing of camp movements are poorly known. We tested the hypothesis that the timing of such moves maximizes foraging efficiency as huntergatherers move across the landscape. The marginal value theorem predicts when a group should depart a camp and its associated foraging area and move to another based on declining marginal return rates. This influential model has yet to be directly applied in a population of hunter-gatherers, primarily because the shape of gain curves (cumulative resource acquisition through time) and travel times between patches have been difficult to estimate in ethnographic settings. We tested the predictions of the marginal value theorem in the context of hunter-gatherer residential mobility using historical foraging data from nomadic, socially egalitarian Batek hunter-gatherers (n = 93 d across 11 residential camps) living in the tropical rainforests of Peninsular Malaysia. We characterized the gain functions for all resources acquired by the Batek at daily timescales and examined how patterns of individual foraging related to the emergent property of residential movements. Patterns of camp residence times conformed well with the predictions of the marginal value theorem, indicating that communal perceptions of resource depletion are closely linked to collective movement decisions. Despite (and perhaps because of) a protracted process of deliberation and argument about when to depart camps, Batek residential mobility seems to maximize group-level foraging efficiency.foraging theory | marginal value theorem | hunter-gatherer | residential mobility | ethnoarchaeology H umans have lived as hunter-gatherers for more than 95% of our species history, moving as individuals and groups in response to variation in the distribution of food in time and space. Food availability is, therefore, central to explaining the logistical and residential (i.e., camp) mobility patterns of huntergatherers (1, 2), a relationship that informs prevailing theories of hominin evolution and human uniqueness (3). Given that residential moves are costly, natural selection should minimize these costs within the bounds of local ecological constraints (4). Consistent with this notion, bioenergetic availability dictates the number of residential moves per year and the distance traveled per move, with foragers in warm, high-productivity environments moving shorter distances more frequently compared with foragers in cool, low-productivity environments (1, 4-6).These group-level macroecological patterns necessarily emerge from the foraging behavior of individuals, but the proximate ecological and social factors that influence these collective movement decisions remain poorly understood (1, 5, 6). One prominent yet untested hypothesis is that selection should optimize the time at which hunter-gatherers abandon camps to maximize foraging efficiency. However, as s...

Foraging Optimally in Social Neuroscience: Computations and Methodological considerations

“…Human hunter-gatherers are a clear example of such behaviours, and there is qualitative evidence of MVT-like behaviour in hunter-gatherer foragers (Smith et al, 1983). Furthermore, using historical foraging data from a nomadic hunter-gatherer society, Venkataraman et al (2017), showed that the 'residential mobility' of a group fits well with MVT predictions. That is, the decision of when to move camp conforms with optimal leaving times based on the local habitat and broader environment in which the group resides.…”

Minimalism and Evolution

“…The emergent hunter-gatherer pattern resulted in long delays between the acquisition and the use of tools, as well as geographical distance between the sources of raw material for tools and killing or butchering sites (Gärdenfors and Osvath, 2010). The hunter-gatherer lifestyle involved frequent shifts of camp as resources were depleted, forcing the group to move on to another more abundant region-a pattern still evident in present-day hunter-gatherers (Venkataraman et al, 2017).…”

Communal and efficient movement routines can develop spontaneously through public information use

“…Animal aggregations can yield some of the most striking spatial patterns in nature. They are observed in almost all taxa (Ims 1988;Sumpter 2006;Bruce and Bradford 2015;Venkataraman et al 2017), and may comprise several species (Heymann and Buchanan-Smith 2000;Goodale et al 2010). In some cases, they result directly from the existence of large-scale resource heterogeneity, but in others, animals aggregate more than what would be expected on the basis of resource distribution alone (Brown and Orians 1970;Jeanson et al 2005).…”