Pyramids of numbers

The population of each organism in a food chain can be shown in a type of bar chart called a pyramid of numbers. The bars are drawn to scale – the more organisms it represents, the wider the bar. The producer in the food chain always goes at the bottom of the pyramid of numbers.

Think about this food chain:

clover → snail → thrush → hawk

Clover is a plant and it is the producer in this food chain. Its bar goes at the bottom of the pyramid:

Food pyramid showing a large number of clover at the bottom, with a slightly smaller number of snails, a smaller number of thrushes and an even smaller number of sparrowhawks on top — Figure caption,
A food chain and the pyramid of numbers that goes with it

Energy is lost to the surroundings as we go from one level to the next, so there are usually fewer organisms at each level in this food chain. A lot of clover is needed to support the snail population. A thrush eats lots of snails, and a hawk eats lots of thrushes, so the population of hawks is very small.

Other pyramid shapes

Sometimes the pyramid of numbers does not look like a pyramid at all. This could happen if the producer is a large plant such as a tree, or if one of the animals is very small. Remember that the producer always goes at the bottom of the pyramid.

Here are two examples of this:

Food pyramid showing a single oak tree, a greater number of insects, and a slightly smaller number of woodpeckers — Figure caption,
An oak tree is very large so many insects can feed on it

Shows a large quantity of grass, a much smaller number of rabbits, and a large number (but not as large as the quantity of grass) of fleas — Figure caption,
Fleas are very small so lots of them can feed on a rabbit

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Interdependency between animal and plant speciesPyramids of numbers