Ecological pyramids

Definition

Ecological pyramids are graphical representations that show the relative amounts of energy or matter contained within each trophic level in a food chain. They can illustrate the number of organisms, biomass, or energy content at different levels of an ecosystem.

5 Must Know Facts For Your Next Test

1. There are three main types of ecological pyramids: pyramid of numbers, pyramid of biomass, and pyramid of energy.
2. Pyramids of energy always show a decrease in energy at higher trophic levels due to the Second Law of Thermodynamics.
3. In a pyramid of biomass, the total mass of organisms decreases as you move up trophic levels; this is typically measured in units like grams per square meter.
4. A pyramid of numbers shows the number of individual organisms at each trophic level; it can sometimes be inverted if smaller organisms are more numerous.
5. Energy transfer between trophic levels is inefficient, with only about 10% of the energy being passed on to the next level.

Review Questions

• What type of ecological pyramid always shows a decrease in quantity as you move up trophic levels?
• Why might a pyramid of numbers be inverted in certain ecosystems?
• What percentage of energy is typically transferred from one trophic level to the next?

Related terms

Trophic Level: The position an organism occupies in a food chain.

Biomass: The total mass of living matter within a given unit area.

Food Chain: A linear sequence through which nutrients and energy pass as one organism eats another.