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Simulating the Tragedy of the Commons Using Agent-Based Modeling

Simulating the Tragedy of the Commons Using Agent-Based Modeling. Josh Lee Computer Systems Lab 08/09. Tragedy of the Commons -autonomous individuals -communal resources Experimental Economics -conventional economic wisdom Agent-Based Modeling -agent types -NetLogo. Abstract.

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Simulating the Tragedy of the Commons Using Agent-Based Modeling

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  1. Simulating the Tragedy of the Commons Using Agent-Based Modeling Josh Lee Computer Systems Lab 08/09

  2. Tragedy of the Commons -autonomous individuals -communal resources Experimental Economics -conventional economic wisdom Agent-Based Modeling -agent types -NetLogo Abstract

  3. Example: Waste -individuals contributing to group problem -finite resources Sahel -three-tier model -more complex, but more realistic/practical The Tragedy ofthe Commons

  4. “Understanding the Tragedy of the Sahel,” Corey L. Lofdahl -original Tragedy of the Commons ABMS “The Tragedy of the Commons,” Garrett Hardin -max goods v. max population -stabilization Background

  5. Sahel, overshoot-and-collapse Individual agent behavior -agent cooperation (or lack thereof); experimental economics -emergent behavior, dominant behavior types System Dynamics v. Agent-Based Modeling

  6. Fig. 1: Model, Upon Opening

  7. Adjustable Parameters “grass-growth-rate” “grass-energy” “cattle-energy” Likelihood of finding resources Example: -greater grass-growth-rate >greater cattle population >lower grass count >greater competition -long-term, greater instability Model Overview

  8. Fig. 2: Population Fluctuations (Instability)

  9. Drought Length, frequency Demonstrates instability Emergent Behavior Dominant behavior type Population stability Further Development

  10. Fig 4: Unique Emergent Behavior

  11. - systematically varies parameters - extensive data output BehaviorSpace

  12. -Stability decreases with increases in grass-energy; begins to have irreversible ramifications around ~17 -Human populations (higher level tier) less stable than cattle populations (lower level tier) BehaviorSpace

  13. -Raised cattle-threshold/people-threshold leads to greater stability -Greater stability leads to more clearly delineated population patterns Behavior Space, cont.

  14. “Greater stability leads tomore clearly delineatedpopulation patterns” V.

  15. Conclusions • -Greatest stability: minimal competition, ability to sustain at a steady population rate • -Stability: ability to counteract perturbances • -Balance between resources, population size, and reproduction rate

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