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Science

Food chains

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Pyramids of numbers

The population of each organism in a food chain can be shown in a sort of bar chart called a pyramid of numbers. The more organisms there are, 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:

cloversnailthrushhawk

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

Shows a large number of clover, a slightly smaller number of snails, a smaller number of thrushes and an even smaller number of sparrowhawks

Energy is lost to the surroundings as we go from one level to the next, so there are 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 doesn't 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, though, that whatever the situation, the producer still goes at the bottom of the pyramid.

Here are two examples like this:

Shows a single oak trea, a greater number of insects, and a slightly smaller number of woodpeckers

An oak tree is very large so many insects can feed on it

Shows a large number of grass, a much smaller number of rabbits, and a larger number (but not as large as the amount of crass) of fleas.

Fleas are very small and lots of them can feed on a rabbit

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