Note: This is post #63 in a weekly video series on basic microeconomics.

Common resources are nonexcludable but rival, says Alex Tabarrok in this video by Marginal Revolution University. For instance, no one can be excluded from fishing for tuna, but they are rival — for every tuna caught, there is one less for everyone else. Nonexcludable but rival resources often lead to what we call a “tragedy of mons.” In the case of tuna, this means the collapse of the fishing stock. Under a tragedy of mons, a resource is often overused and under-maintained. Why does this happen?

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