What Is an Energy Pyramid?
An energy pyramid (also called a trophic pyramid) is a diagram that shows how energy is distributed among the different feeding levels — called trophic levels — in a food chain or food web.
The pyramid is always widest at the base (producers) and narrowest at the top (top carnivores). This shape reflects the fact that energy is lost at each level.
Trophic Levels
| Level | Who | Example |
|---|---|---|
| 1st (base) | Producers | Grass, algae, trees |
| 2nd | Primary consumers (herbivores) | Rabbits, insects, deer |
| 3rd | Secondary consumers | Foxes, frogs, small fish |
| 4th | Tertiary consumers (top predators) | Eagles, sharks, wolves |
The 10% Rule
When energy passes from one trophic level to the next, roughly 90% is lost and only 10% is transferred.
Energy is lost as:
- Heat — from cellular respiration (all organisms constantly release heat)
- Waste — undigested food passes out as faeces
- Movement — energy used for muscles, digestion, and other processes
This means:
- If plants capture 10 000 kJ of energy from sunlight
- Herbivores get ≈ 1 000 kJ
- Secondary consumers get ≈ 100 kJ
- Top predators get ≈ 10 kJ
This is why eating lower on the food chain is more energy-efficient. Growing 1 kg of beef requires about 10 kg of grain (and the grain requires a lot of water, land, and fertiliser). Eating plant foods directly uses far less energy and land per calorie.
Why Are Food Chains Short?
The 10% rule explains why food chains rarely have more than four or five levels. By the fourth trophic level, so little energy remains that only a very small number of top predators can survive.
Biomass Pyramid
A closely related concept is the biomass pyramid, which shows the total mass of organisms at each level. It has the same shape (usually) — most biomass is in producers, least in top predators. This is why there is more grass than rabbits, and more rabbits than foxes in a meadow.
To remember the 10% rule: imagine energy as money. Each time it changes hands in a food chain, 90% goes in "taxes" (heat and waste). The next animal only gets 10 cents for every £1 the previous level had.
Real world: Meat production and land use
The 10% rule explains why beef farming requires enormous amounts of land. It takes roughly 10 kg of grain to produce 1 kg of beef — because the cow loses 90% of the grain's energy to heat and movement. This is why switching from meat-heavy to plant-based diets can significantly reduce the land and water needed to feed the same number of people.
Real world: Why there are more mice than owls
In a meadow at night, there are many thousands of mice but only a handful of barn owls. The energy pyramid explains this: owls are tertiary or secondary consumers and only receive a small fraction of the energy that starts with the grass. The ecosystem simply cannot support large numbers of top predators because so little energy reaches that level.
Real world: Fish farming efficiency
Salmon farms feed their fish on smaller fish (like herring), making salmon secondary consumers. Each tonne of salmon produced requires several tonnes of herring — the 10% energy loss in action. This is why some fish farmers are switching to algae-based feeds that put salmon at a lower trophic level, using less energy to produce the same amount of food.
Where do you see this in real life? Every time you see a wildlife documentary showing vast herds of wildebeest and only a few lions, you are seeing the energy pyramid. Large producers at the base support fewer and fewer animals as you move up the food chain — the shape is always a pyramid, never inverted.