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School Biology GCSE level exam revision notes: 5. Pyramids of numbers

5. What is a pyramid of numbers in a food chain? How do you construct a pyramid of numbers - examples explained and illustrated

[Author © Dr WP Brown PhD: Doc Brown's biology exam revision notes suitable for students of UK IGCSE & GCSE level biology courses & ~ US grades 9-10 biology, page updated Feb 6th 2026 *]

[Key points and learning objectives for this page, after the main body of notes]

Sub-index of Biomass, energy. pyramids, food web notes

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(5) Pyramids of numbers of individuals - how to construct them - examples explained

Construction of pyramids of numbers (NOT biomass).

Pyramids of numbers are similar to pyramids of biomass but each bar represents the relative total number of individuals in a population for one of the organisms in a food chain, NOT their total mass.

Although a pyramid of numbers can be the same shape as a regular pyramid shape of biomass, it is quite often a very different shape and not really a pyramid.

For example a bird feeds off caterpillars on a large cabbage plant. One small bird might feed on 25 caterpillars on one large cabbage plant. The 'non-pyramid' of numbers looks like the left-hand diagram below.

Pyramid of numbers (above and the pyramid of biomass for the same food chain (below)

This shape is rather different for the pyramid of biomass for the same food chain (shown right-above).

 

However, in the case of another food chain e.g. in a freshwater lake/stream/river system:

Pondweed eat by tadpoles ==> eat by water beetles ==> perch fishes eat water beetles ==> otter eats perch

The pyramid of numbers is the same shape as the pyramid of biomass

Pyramid of numbers

Comparing the pyramid of biomass for the same food chain

 

More examples of pyramids of numbers

u = producer,  v = primary consumer,  w = secondary consumer, x = tertiary consumer numbers

Pyramid of numbers 1 food chain examples

mosses => beetles => birds => sparrowhawk

algae => crabs => seals => eskimos

Pyramid of numbers 2 food chain examples

grass => rabbits => foxes => fleas

grasses => zebra => lion => fleas

Pyramid of numbers 3 food chain examples

grass => cattle => ticks => birds

grass => antelope => mites => birds

Pyramid of numbers 4 food chain examples

rose bush => greenfly => ladybirds => swallows

tree => beetles => mice => owls

Pyramid of numbers 5 food chain examples

fruit bush => caterpillars => birds => fleas

tree => monkeys => tigers => mosquitos

Key points - Summary of ideas

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

A pyramid of numbers is a graphical representation of the number of organisms at each trophic level in a food chain.

It shows how population sizes change as you move up the food chain from producers to apex predators.

Understanding the Pyramid of Numbers

Each level represents a trophic stage:

  • Producers (plants) form the base and usually have the highest numbers.

  • Primary consumers (herbivores) are fewer in number than producers.

  • Secondary consumers (carnivores that eat herbivores) are even fewer.

  • Tertiary consumers (top predators) are the least numerous.

This pattern can vary, especially in cases like parasites, where many tiny organisms feed on a single host, making the pyramid inverted.

How to Construct a Pyramid of Numbers

  1. Identify the organisms in the food chain. Example: grass → rabbit → fox.

  2. Count the number of organisms at each trophic level. Example:

    • Grass: 500

    • Rabbits: 50

    • Foxes: 5

  3. Draw a pyramid shape. The width of each level represents the number of organisms.

    • The base is the widest (representing producers).

    • The next level is narrower (primary consumers).

    • The higher levels keep narrowing.

This pyramid visually emphasizes the decreasing number of organisms as you move up the food chain.

Summary of learning objectives and key words or phrases

Know how do you construct a pyramid of numbers for a food chain of plants and animals.

Be able to explain the relationship between plants and animals for a pyramid of numbers.

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