The idea
Energy enters almost every ecosystem on Earth as sunlight, gets captured by producers, and then moves up through the organisms that eat them. At every step, most of it is lost as heat.
The ten percent rule
Roughly 10% of the energy at one trophic level ends up stored in the next. The rest was spent staying alive, or never eaten in the first place.
Start with 10 000 kJ captured by plants in a field:
| Trophic level | Energy available |
|---|---|
| Producers (grass) | 10 000 kJ |
| Primary consumers (grasshoppers) | 1 000 kJ |
| Secondary consumers (frogs) | 100 kJ |
| Tertiary consumers (hawks) | 10 kJ |
Why are there no ten-level food chains?
Work the arithmetic down another few rows and you will answer this yourself. There is simply nothing left to support the tenth level.
That is also why a pyramid is the right shape for this diagram, and why eating lower on the food chain feeds more people from the same land.
Curriculum connection
B2.2
explain how naturally occurring phenomena, including the cycling of matter and the flow of energy, contribute to the dynamic equilibrium within and between ecosystems
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B2.3
compare and contrast the processes of cellular respiration and photosynthesis, and explain how their complementary relationship contributes to the dynamic equilibrium of ecosystems
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