Pyramids of number and biomass

The number of organisms in each trophic level is counted and presented in a pyramid of numbers.

These are referred to as pyramids because of their shape.

Producers have a higher value than the primary consumers; primary consumers have a higher value than the secondary consumers and so on.

Advantages	Disadvantages
Counting numbers is easy to do.	They do not take the organism’s size into account so may not always resemble a pyramid. For example, if producer is 1 tree then pyramid will look inverted (smaller on bottom).

Advantages	Counting numbers is easy to do.
Disadvantages	They do not take the organism’s size into account so may not always resemble a pyramid. For example, if producer is 1 tree then pyramid will look inverted (smaller on bottom).

The biomass (amount of living material) of organisms in each trophic level is measured and presented in a pyramid of biomass.

Advantages	Disadvantages
It is more accurate as the organism’s size is taken into account. For example, a bar representing 1 tree will be largest as it has more mass than primary consumers.	Biomass data is difficult to obtain as the organism needs to be killed and heated in an oven to remove any water, until a constant dry mass is obtained.

Advantages	It is more accurate as the organism’s size is taken into account. For example, a bar representing 1 tree will be largest as it has more mass than primary consumers.
Disadvantages	Biomass data is difficult to obtain as the organism needs to be killed and heated in an oven to remove any water, until a constant dry mass is obtained.

Pyramids of biomass are used to overcome the problem of inverted pyramids of number.

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