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Jacob Freeman (ASU) Mutual feedback between resource base and foraging decisions on the evolution of hunter-gatherer societies
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Jacob Freeman (ASU) Mutual feedback between resource base and foraging decisions on the evolution of hunter-gatherer societies

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  • 1. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionIntensification, Tipping Points, and Social Change in a Coupled Forager-Resource System Jacob Freeman1 John M. Anderies 1 1 The School of Human Evolution and Social Change Arizona State University CUNY Human Ecodynamics Workshop Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 2. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionOutline 1 Motivation 2 The Foraging Effort Model 3 Analysis: Resilience and Social Change 4 Discussion Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 3. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionQuestion Question: Given the open-access nature of resources among hunters and gatherers, if individual foragers extract more resources per unit area, how does this behavior impact the resilience of a forager-resource system? Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 4. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionBasic Assumptions 1 Foragers groups primarily exploit open-access resources within a habitat and this habitat is embedded in a landscape of habitats 2 The interpretation of the model is restricted to the use of stationary resources 3 Forager population density is a parameter 4 Foraging effort (e) is interpreted as time spent harvesting resources (workdays per day) 5 Two energy targets motivate behavior, c and γ Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 5. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionResource Growth and Harvest x G(x) = rx(1 − ) (1) K resource growth rate 0 resource density K Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 6. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionResource Growth and Harvest H(x, e) = ph(x, e) (2) h(x, e) = qxe (3) Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 7. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Conversion of Biomass to Energy α = le(−mp) (4) efficiency of converting biomass into energy (α) 1 m = 0.5 m = 0.8 0 forager group density (p) Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 8. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Conversion of Biomass to Energy α = le(−mp) (4) efficiency of converting biomass into energy (α) 1 m = 0.5 m = 0.8 0 forager group density (p) Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 9. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionTime Allocation δ = γ − αh(x, e) (5) 16 Jacob Freeman, John M. A 1 Region 2a. Resource density is high enough to meet basic metabolic needs. Thus, foragers attempt Region 1. Resource density is so low to meet their daily energy goal of g by changing that more foraging effort is required to effort in proportion to their energy deficit. That is Foraging deficit, d meet basic metabolic needs than for- D(x, e) ⇡ a1 d so that de/dt ⇡ a1 d . Here, d > 0 so agers are willing to tolerate (or are cap- foraging effort will increase. bable of). Foragers reduce effort at a 0 constant rate. That is, D(x, e) ⇡ a2 so that de ⇡ a2 . dt Region 2b. As in Region 2a, but here, d < 0 so foraging effort will decrease. -1 0 c 3 Harvest per unit foraging effort, ah(x, e)/e Fig. 2 Foraging effort decision dynamics. The different regions in the daily energy deficit - daily energy harvest plane generate a simple d heuristic for forager groups. See Box 2 for the mathematical details of the function used to represent these different regions. Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 10. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Story dx = G(x) − H(x, e) (6) dt de = D(x, e). (7) dt Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 11. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Maximally Resilient System: p=0.5 2.5 a 2 foraging Effort 1.5 Foraging effort 1 (S) (S) 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Resourcedensity resource Density Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 12. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Resilient but Vulnerable System: p=0.7 2 (Z) bb (U) (Z) 1.5 foraging Effort (U) Foragingeffort 1 (S) (S) 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 resource density Resource Density Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 13. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionThe Degraded System: p=0.8 2 (Z) cC 1.5 (Z) foraging Effort Foragingeffort 1 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Resource Density resource density Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 14. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionInstitutions and Windows of Vulnerability . 00 . 20 . 40 . 60 . 80 1. 00 1. 20 1. 40 window of vulnerability 1. 40 equilibrium foraging effort (e*) 1. 20 1. 20 1. 00 1. 00 αh(x,e)/e = c . 80 . 80 αh(x,e)/e > c . 60 . 60 . 40 . 40 . 20 . 20 . 00 . 20 . 40 . 60 . 80 1. 00 1. 20 forager group density (p) Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 15. Motivation The Foraging Effort Model Analysis: Resilience and Social Change DiscussionInstitutions and Windows of Vulnerability . 00 . 20 . 40 . 60 . 80 1. 00 1. 20 1. 40 window of vulnerability 1. 40 equilibrium foraging effort (e*) 1. 20 1. 20 1. 00 αh(x,e)/e = c 1. 00 . 80 . 80 . 60 αh(x,e)/e > c . 60 . 40 . 40 . 20 . 20 . 00 . 20 . 40 . 60 . 80 1. 00 1. 20 forager group density (p) Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 16. Motivation The Foraging Effort Model Analysis: Resilience and Social Change Discussion1 The very success of an adaptation at the level of an individual forager group can create system-level vulnerabilities that subsequently feed back to cause emergent social change.2 A looming tipping point creates uncertainty and associated risk for foragers.3 Alternatives adaptive strategies: relocate, reform or control4 Freeman, J. and Anderies J. M. 2012. Intensification, Tipping Points, and Social Change in a Coupled Forager-Resource System. Human Nature (DOI) 10.1007/s12110-012-9154-8 Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 17. Motivation The Foraging Effort Model Analysis: Resilience and Social Change Discussion1 The very success of an adaptation at the level of an individual forager group can create system-level vulnerabilities that subsequently feed back to cause emergent social change.2 A looming tipping point creates uncertainty and associated risk for foragers.3 Alternatives adaptive strategies: relocate, reform or control4 Freeman, J. and Anderies J. M. 2012. Intensification, Tipping Points, and Social Change in a Coupled Forager-Resource System. Human Nature (DOI) 10.1007/s12110-012-9154-8 Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers
  • 18. Motivation The Foraging Effort Model Analysis: Resilience and Social Change Discussion1 The very success of an adaptation at the level of an individual forager group can create system-level vulnerabilities that subsequently feed back to cause emergent social change.2 A looming tipping point creates uncertainty and associated risk for foragers.3 Alternatives adaptive strategies: relocate, reform or control4 Freeman, J. and Anderies J. M. 2012. Intensification, Tipping Points, and Social Change in a Coupled Forager-Resource System. Human Nature (DOI) 10.1007/s12110-012-9154-8 Jacob Freeman, John M. Anderies The Resilience of Hunter-Gatherers