Marvin Soroos
North Carolina State University
The Commons Game
Purpose: To achieve through role playing a deeper understanding of how the "tragedy of the commons" takes place and to experiment with strategies for avoiding an overshoot of the carrying capacity of a limited resource.
Each student plays the role of a herder in an old English village who owns one cow that he grazes on the community pasture. So long as the pasture is not being overgrazed, each cow provides its owner with an income of 30 monetary units (MUs) each round. The accumulated wealth may be used to purchase additional cattle at a cost of 40 MUs per head.
The carrying capacity of the pasture is reached when the size of the village herd exceeds its original size by a factor of two and one half. Thus, if there are twenty herders, the carrying capacity is assumed to be 50. When the carrying capacity is exceeded, the income derived from each head of cattle is reduced depending on the number of excess cattle that are being grazed.
It is suggested that the game be played twice. In the playing of the first run, each time period should follow immediately after the preceding one without time for the participants to interact with one another. During the second run, they should be allowed a five minute town meeting after every second time period. During these town meetings, the participants may adopt a strategy for limiting the number of cattle being grazed on the pasture.
As each round progresses the participants are to complete the calculations outlined on the talley sheets that are provided. Each time period begins with the participants figuring their income from the previous period. The director informs the herders of the cost of the overgrazing for the period, which is to be entered in line 2. If the total number of cattle is less than 2.5 times the number of herdsmen, the cost of overgrazing is zero. If it is more than 2.5, the Cost of Overgrazing Table should be checked for the applicable figure, taking into account the number of participants and the number of excess cattle. The actual profit per head (line 4) is then calculated by subtracting the cost of overgrazing (line 2) from the potential profit per head (line 1), which is a constant 30 MUs.
The next step is for each herder to enter the number of cattle they own at the beginning of the period on line 4, which is calculated by adding the number of new cattle purchased during the previous round (line 4). All herders begin the run with one cow. The resulting figure is multiplied by the actual profit per head (line 3) to calculate the income for the round, which is entered on line 5. The number of MUs carried over from the previous round (line 13), assumed to be 0 in Round 1, is entered on line 6 and added to the income for the current round (line 5) to calculate the accumulated wealth (line 7) of the herdsman. Line 8 contains a cost of living figure which is a contant 50 MUs. It is subtracted from the accumulated wealth (line 7) and the resulting figure, referred to as net operating expenses, is entered in line 9.
The participants may then elect to use part or all of their net operating funds to purchase additional cattle at a cost of 40 MUs per head as indicated on line 10 and multiplied by line 11 to calculate the expenditures for cattle, which is entered on line 12. The number of MUs remaining at the end of the current round (line 13) is then calculated by subtracting the expenditures for cattle (line 12) from the accumulated wealth (line 9).
The director may interject complicating factors. For example, it may be announced that a drought is taking place in which the cost of overgrazing figure is selected from the row below the one that would normally be used. Another pissibility is to have additional herder joing the fame while it is in progress, yet use the same column in the Cost of Overgrazing Table.
Cost of Overgrazing Table
ª carrying capacity = number of herdsmen x 2.5
° If there are more than 20 students in the class, separate games should be organized for groups of 10-20
Questions following the first run:
1. What was the outcome of the first round? Did a "tragedy" occur?
2. Did any of the herders voluntarily limit the size of their herds?
3. If there was a voluntary restraint on the part of the herders, did it contribute to an averting of a "tragedy"? Or did other herders take advantage of the restraint?
Questions following the second run:
1. Did a "tragedy" occur in the second run of the game?
2. What strategies were adopted at the town meetings to avert a tragedy?
3. Were difficulties encountered in devising a strategy?
4. Were mandatory limits imposed upon the herders either individually or collectively? If so, what form did they take?
5. If mandatory limits were imposed, were problems encountered in enforcing them?
6. What other strategies can you think of that would have potential for averting a tragedy?
7. Would it have been more difficult to come up with a solution to the tragedy problem if the herdsmen had not had equal numbers of cattle at the
beginning?
Talley Sheet
Talley Sheet - 2 Per Herdsman
Talley Sheet - Unrestricted Herds
Talley Sheet - Free Rider (Everybody else limits to two)