4% Rule (retirement)

Biological Parallel

Wolf packs harvest roughly 4-5% of their elk population annually—the maximum sustainable yield that allows prey recovery without depleting the herd. Take more and the population crashes; take less and you waste available resources while competitors move in. This 4% threshold appears across ecosystems as the equilibrium between current consumption and future availability, from predator-prey systems to forest harvesting. It's not conservative planning; it's the mathematical boundary where resource extraction matches regeneration rate.