The meadow catches sunlight, mice eat plants, owls eat mice — but each step passes on only a fraction of the energy, most lost as heat. That's why there are countless plants, many mice, and only a few owls.
Energy flows one way
Energy enters ecosystems as sunlight, which producers (plants) capture. It then flows to consumers along a food chain: producer → primary consumer → secondary consumer. Each step is a trophic level. Unlike nutrients, energy is not recycled — it dissipates as heat at every level.
Only about 10% of the energy at one trophic level is passed to the next; the rest is used for life processes or lost as heat. That is why food chains rarely have more than four or five links.
Grass (100 units) → grasshopper (~10) → frog (~1) → snake (~0.1). Energy shrinks tenfold each step.
- A plant captures 1000 units of energy.
- Apply the 10% rule to the primary consumer.
- Estimate the energy reaching the secondary consumer.
What you should see: The primary consumer gets ~100 units, the secondary ~10 — energy drops about tenfold at each trophic level.