Read Ecological Pyramids by What Is Counted
A pyramid changes shape depending on whether it counts organisms, biomass or energy and on the ecosystem sampled.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Compare pyramid types
Numbers can be inverted in a tree or parasitic chain. Biomass can be inverted in aquatic ecosystems because small phytoplankton turn over quickly. Energy pyramids are always upright because usable energy decreases at every transfer.
Use trophic-level constraints
Higher trophic levels usually contain fewer organisms and less available energy. The second law of thermodynamics explains why energy cannot increase upward through a food chain.
Recognise inverted pyramids of number
A single tree can support many herbivorous insects, and hosts can support even more parasites. Both a tree ecosystem and a parasitic food chain can therefore show an inverted pyramid of numbers. Always identify whether a figure counts individuals, biomass, or energy before naming its shape.
Read a terrestrial biomass pyramid
A tree carries the largest biomass, birds less, and parasites least. The correct source shape therefore narrows from bottom to top. Do not confuse this with the inverted pyramid of numbers seen in many parasite chains.
OlympIQ exam lens
- ✓Number pyramids may be upright or inverted.
- ✓Aquatic biomass pyramids may be inverted.
- ✓Energy pyramids are always upright.
- ✓Higher trophic levels receive less energy.
Do not generalise the shape of one pyramid type to the others.
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