Pyramids of numbers show stages in a food chain.
Each level on a pyramid of numbers is called a trophic level.
Pyramids of biomass show the total dry mass of the organisms at each trophic level.
Pyramids of numbers are not always pyramid shape whereas pyramids of biomass are.
Data for pyramids of biomass must be obtained from dry mass, so the organisms have to be killed. Therefore only a small sample can be used which may not be representative.
Pyramids of energy are produced by sampling and burning the organisms from each trophic level in a calorimeter, to determine how much heat energy is produced per gram.
This is very time-consuming and very destructive to the environment.
They only take a snapshot of an ecosystem at one moment in time.
Pyramids of energy are always pyramid shaped because energy is lost at each level, so the size of each bar decreases at each successive trophic level.

	Created by b187083 over 8 years ago

food chains, food webs, pyramids

Food Webs