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How to apply the 10% rule in food chains

Energy moves between trophic levels, but only about 10% transfers upward. Here is how to compute energy at each level of a food chain.

Food chains transfer energy from producers to consumers, but inefficiency is huge: roughly 90% is lost as heat at every step. Only about 10% moves to the next trophic level.

The rule

Enext=Ecurrent×0.1E_{\text{next}} = E_{\text{current}} \times 0.1

Worked example

Producers capture 50,00050{,}000 kcal.

  • Primary consumers: 50,000×0.1=5,00050{,}000 \times 0.1 = 5{,}000 kcal
  • Secondary consumers: 5,000×0.1=5005{,}000 \times 0.1 = 500 kcal
  • Tertiary consumers: 500×0.1=50500 \times 0.1 = 50 kcal

That is why few top predators exist: each level shrinks by a factor of ten. Practise on randomised energy-pyramid questions below.

Put it into practice

Practise this topic with questions and get an explanation after each answer.

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