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

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

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

4. Background “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
”Artificial Agents Learning Human Fairness”
- 'Continuous Action Learning Automata' and the 'Homo Equalis utility function'
-quantative evaluation

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

6. Fig. 1: Model, Upon Opening

7. Model Overview 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

8. Fig. 2:
Population
Fluctuations
(Instability)

9. Additional Features Drought Length, frequency Demonstrates instability
Behavior Alterations
Degrees of altruism (behavior types)
Expand awareness
-available grass, people

10. Future Development Homo Egualis Utility function
Numerically evaluate success
Emergent Behavior
Dominant behavior type
Population stability

11. Problems Difficulty managing population trends
Cattle populations unstable
-sustaining losses appropriately
-recovering over an appropriate time span
Difficulty implementing awareness/altruism

13. Fig 4: Unique Emergent Behavior