Pyramids of Numbers Or Pyramids of Biomass

Pyramids of numbers or pyramids of biomass?

Pyramids of numbers and pyramids of biomass are both used to show feeding relationships between organisms in an ecosystem. Below are three different ecosystems. On graph paper, draw a pyramid of numbers and a pyramid of biomass for each ecosystem. Remember, the length of each bar shows the numbers in pyramids of numbers, and the area shows the biomass present in pyramids of biomass.

Make sure all your bars are to scale.

Ecosystem 1 - A hedgerow

Ecosystem 2 - An oak tree

Ecosystem 3 - Grassland

As you can see, pyramids of numbers are not always 'pyramid shaped'. If they are not, they are called 'inverted pyramids'. When do you get inverted pyramids of numbers?

• From what you have drawn, can you say whether pyramids of biomass are usually 'pyramid shaped'?

• Which type of pyramid do you think represents the 'quantity' or

amount' of organisms within the food chain most accurately?