3. The Energy Pyramid & the 10% Rule

Energy doesn't pass perfectly from one level to the next — most of it is lost along the way. An energy pyramid shows how the energy available shrinks at each higher feeding (trophic) level.

A useful rule of thumb is the 10% rule: only about 10% of the energy at one level is passed to the next. The other ~90% is used to live (movement, growth, body heat) and lost as heat. So if producers capture 10,000 kcal, primary consumers get about 1,000, secondary consumers about 100, and the top level only about 10.

This is why ecosystems have many producers but few top predators, and why food chains rarely have more than four or five links — there simply isn't enough energy left to support more.

⚠️ Common misconception: energy is not recycled the way matter is. Energy flows through an ecosystem and is eventually lost as heat — it does not return to the producers to be used again.

💡 Tip: remember 'matter cycles; energy flows.' Energy drops by about 90% at each step up the pyramid.