Pyramids of Numbers & Biomass
Pyramids of numbers
- Pyramids of numbers are diagrams used to visually represent the number of individual organisms present at each stage of a food chain
- Pyramids of numbers can vary in shape depending on the food chain in question
- Small individuals will be many in number
- Large individuals will be few in number
- Pyramids of numbers should have the following features:
- Name labels for each trophic level
- Labels to indicate the number of individuals at each trophic level
- Some pyramids of numbers may be drawn to scale, meaning that the size of the bar is proportional to the number of individuals
- An exam question in which a grid has been provided will require any pyramids to be drawn to scale; see below for an example
Pyramid of numbers diagram
Pyramids of numbers show the number of individuals at each stage of a food chain; they should be labelled with the name of each level and the number of individuals represented by each bar
Pyramids of biomass
- Pyramids of biomass show the mass of living tissue present at each stage of the food chain
- Pyramids of biomass are always pyramid-shaped, meaning that the bars decrease in size from the base to the top of the pyramid
- This is because of the energy losses at each stage of a food chain; there is less energy available for the production of new biomass at higher trophic levels
- Just as with pyramids of numbers, pyramids of biomass should always be clearly labelled to indicate the trophic level and the biomass represented by each bar
- If a grid is provided then the pyramid should be drawn to scale
Pyramid of biomass diagram
Pyramids of biomass represent the mass of living material at each stage of a food chain; they are always pyramid shaped due to losses at each trophic level
Worked example
Fig. 1 shows a food chain with four trophic levels. Biomass for each organism is shown below in kg.
Fig. 1
Clover | → | Snail | → | Thrush | → | Sparrowhawk |
80 | 30 | 10 | 2 |
Draw a pyramid of biomass for the food chain shown in Fig. 1