What is overshoot and collapse?

Overshoot and collapse happens when growth continues beyond a sustainable level because the signal that warns of the limit arrives late, or because the limit itself is being consumed. The result is a peak followed by a steep decline, often to a lower level than before. It matters because the damage may be hard to repair.

How it works

There are three ingredients: growth, a limit, and a delay in noticing the limit. While the stock of resources looks plentiful, nothing signals trouble, so growth keeps going. When the shortage finally becomes visible, the population is already too large for what remains. Worse, if the population erodes the resource base, the limit itself drops, so the eventual level is lower than it would have been. Policies that react only to current conditions, not to trends, tend to produce this pattern.

Prevention works best by shortening the delay in the signal, or by making consumption respond to the state of the resource, not just to current income. Both make the system turn earlier, before the stock is badly damaged.

Example

Say a fishing region has a stock of 10,000 fish that regenerates about 10 percent a year, roughly 1,000 fish. The fleet grows because catches look good and starts taking 2,500 fish a year. The stock falls by about 1,500 a year, so after three years it holds about 5,500 and regenerates only about 550 a year. Even a fleet that returns to a sustainable catch of 550 must now take far less than before. This is an illustration with round numbers.

How to model it in Machinations

Use a Pool for the renewable resource with a Source for regeneration set by a Register. Add a Pool for the population that consumes it, with a Drain from the resource. Connect them with state connections and put a Delay on the information. Play the diagram with charts of both Pools, then lengthen the delay with a Lever to see the peak get higher and the fall steeper.