Ecological pyramids are diagrams that show how organisms in an ecosystem are arranged by feeding level, or trophic level. They help scientists compare producers, herbivores, carnivores, and top predators in a clear visual way. These pyramids matter because they reveal how energy, matter, and population size change as you move up a food chain.
A pyramid can show why ecosystems usually support many plants but fewer large predators.
Key Facts
- Trophic level 1 contains producers, such as plants, algae, or phytoplankton.
- Energy pyramids show energy flow and are usually upright because energy is lost at each transfer.
- Only about 10% of energy is passed to the next trophic level, often written as ecological efficiency = energy transferred / energy available × 100%.
- Biomass pyramids show total living mass at each trophic level, commonly measured in g/m² or kg/m².
- Numbers pyramids show the number of individual organisms at each trophic level and can be inverted when a few producers support many consumers.
- Energy available at level n can be estimated by E_n = E_1 × 0.10^(n - 1) when using the 10% rule.
Vocabulary
- Trophic level
- A trophic level is a feeding position in an ecosystem, such as producer, primary consumer, or secondary consumer.
- Producer
- A producer is an organism that makes its own food, usually by photosynthesis, and forms the base of most food chains.
- Biomass
- Biomass is the total mass of living organic material in a specific area or trophic level.
- Energy pyramid
- An energy pyramid is a diagram that shows how much energy is available at each trophic level.
- Inverted pyramid
- An inverted pyramid is an ecological pyramid where a higher trophic level has a larger value than the level below it.
Common Mistakes to Avoid
- Assuming all ecological pyramids must be upright is wrong because biomass and numbers pyramids can be inverted in special ecosystems.
- Confusing biomass with number of organisms is wrong because biomass measures total living mass, not how many individuals are present.
- Using the 10% rule as an exact law is wrong because real energy transfer efficiency varies among ecosystems and species.
- Putting decomposers as only one simple pyramid layer is wrong because decomposers act on material from all trophic levels.
Practice Questions
- 1 A grassland has 20,000 kJ of energy stored in producers. Using the 10% rule, how much energy is available to primary consumers, secondary consumers, and tertiary consumers?
- 2 A pond sample has producer biomass of 400 g/m² and herbivore biomass of 60 g/m². What percentage of producer biomass is represented by the herbivore biomass?
- 3 Explain why a pyramid of numbers for a forest with one large oak tree, hundreds of caterpillars, and several birds could be inverted at the producer level.