Many different types of resources are shared by groups of people and it can be a challenge to avoid overharvesting of the commons. For example, consider fishers fishing the oceans, farmers pumping up groundwater, oil companies drilling for oil, or movie watchers using the limited bandwidth of the community internet connection. In 1968 biologist Garrett Hardin wrote a famous essay in the journal Science titled “The Tragedy of the Commons.” He used the metaphor of sheep herders sharing a meadow. While each herder will benefit as an individual from adding an extra sheep to the meadow, as a group they will bear the costs of the additional grazing and especially when it creates a situation in which grazing occurs faster than the resource can be regenerated. The effect of overgrazing is shared by all herders, but the benefit of the extra sheep goes to the sole owner of the sheep.
To avoid overharvesting of the resource Hardin argued that there is a need for strict governmental regulation or privatization of the resources. Without these interventions the herders would inevitably overharvest. Hardin’s essay was highly influential among emerging environmentalists who were becoming increasingly concerned with the many human-caused, environmental problems. They called government to action and new regulations were written to reduce pollution and avoid overharvesting.
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Figure 1: Garrett Hardin.*
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Figure 2: Elinor Ostrom.*
Since Hardin’s essay, an increasing awareness also emerged that a tragedy is not the only possible outcome when people share a common resource. There are many examples of long-lasting communities who have maintained their common resources effectively. Since the 1980s there has been an increasing interdisciplinary effort to debunk the simplistic view of the tragedy of the commons. Elinor Ostrom and others showed through comparative analysis of many case studies that humans can self-govern their common resources. In her classic study “Governing the Commons” Elinor Ostrom defines eight principles that enhance the likelihood of self-governance including effective monitoring and strict boundaries of the resource.
The study of the commons is a broad interdisciplinary research field. Although the main focus has been on environmental resources, applications to health care, digital commons and traffic have been explored.
In this chapter we show through some simple models what happens when agents are greedy, what happens when they imitate other successful agents and what happens when monitoring is included.