Pyramids of energy

Organisms and their environment · Trophic levels and ecological pyramids · note 3 of 4

Spec 19.2.15, 19.2.16

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Pyramids of energySpec 19.2.15, 19.2.16

A pyramid of energy shows the amount of energy that flows through each trophic level in a given area over a period of time, for example in kJ per m² per year. It is drawn in the same way as the other pyramids, with the producers at the bottom and bars drawn to scale.

Example data for a pyramid of energy (practice values)
Trophic level	Energy / kJ per m² per year
Producers	10 000
Primary consumers	1 000
Secondary consumers	100
Tertiary consumers	10

Pyramid of energy drawn to scale: producers 10 000, primary consumers 1 000, secondary consumers 100 and tertiary consumers 10 kJ per m² per year, with a scale bar for 1 000 kJ per m² per year. — A pyramid of energy is always pyramid-shaped. In this example only a tenth of the energy passes on to each higher trophic level.

Advantages of a pyramid of energy

It is always pyramid-shaped, because energy is lost at each trophic level. It cannot be inverted.
It takes into account the size of the organisms, unlike a pyramid of numbers.
It shows the rate of energy flow, over a period of time. A pyramid of biomass shows only the mass at one moment (a pyramid of biomass can be inverted if organisms grow and reproduce quickly, for example algae in the sea).
Different tissues contain different amounts of energy per gram (fat contains more than carbohydrate), so equal biomass does not always mean equal energy. A pyramid of energy compares the energy directly.
It allows the efficiency of energy transfer between trophic levels to be compared.

Exam tip:

Write the units as energy per area per time, such as kJ per m² per year. A pyramid of energy never has an inverted shape.