Pyramids of biomass

Biomass

The dry mass of an organism is called its biomass. The total biomass at a particular step in a food chain is always less than the total biomass at the step before it. Let's look again at the food chainfood chain: A sequence (usually shown as a diagram) of feeding relationships between organisms, showing who eats what and the movement of energy through trophic levels.:

grass → vole → barn owl

The biomass of all the grass plants is the greatest in the chain, and the biomass of all the barn owls is the least. We can show information like this using a pyramid of biomass.

Pyramids

Let's look at a more complex food chain:

oak tree → caterpillar → blue tit → sparrow hawk

Oak trees are very large, but caterpillars are very small. One oak tree can feed many caterpillars, but many caterpillars are needed to feed a blue tit, and many blue tits are needed to feed a sparrow hawk. If we draw a pyramid of numbers for this food chain, it looks like pyramid 1. Note there's only one oak tree, but lots of caterpillars indicated by the shape of the pyramid.

The wider the bar, the more organisms there are. Remember that energy is lost at each step in a food chain.

Pyramid of numbers

Pyramid of biomass

If we draw a pyramid of biomass, it looks like pyramid 2. Note the large biomass of the one oak tree, compared with the small biomass of lots of caterpillars, indicated by the shape of the pyramid.

The wider the bar, the more biomass there is. Pyramids of biomass always have this shape (but pyramids of numbers can be any shape).