Ecological Pyramids
An ecological pyramid is a graphical representation of the number, biomass or energy content of organisms at successive trophic levels in an ecosystem.
In one line: Energy pyramid always stands; number and biomass can sometimes turn.
Concept Practice Coming SoonUnderstand it
- Ecological pyramids help students compare trophic levels visually.
- The base usually represents producers, followed by primary, secondary and tertiary consumers.
- A pyramid of number shows the count of organisms, a pyramid of biomass shows standing crop or dry mass, and a pyramid of energy shows energy flow per unit area per unit time.
- Pyramids of number and biomass may be upright or inverted depending on the ecosystem.
- For example, a tree ecosystem may have an inverted pyramid of number, while an aquatic ecosystem may show an inverted pyramid of biomass.
- The pyramid of energy is always upright because energy decreases at each trophic transfer.
Example
Rule to remember
Key rule: energy pyramid is always upright due to the 10 percent energy transfer pattern; number and biomass pyramids may be upright or inverted depending on organism size and ecosystem type.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1In an aquatic ecosystem, phytoplankton may have low standing biomass at a given moment but reproduce rapidly and support larger zooplankton biomass.
- 2This explains why biomass pyramids in aquatic systems can be inverted.
Method you can reuse
- 1Identify which pyramid is asked: number, biomass or energy.
- 2Place producers at the base.
- 3Add consumers in trophic order.
- 4Decide upright or inverted based on ecosystem and parameter.
- 5For energy, always draw upright and explain energy loss.
Sketch it in your answer
Draw separate pyramids for number, biomass and energy. Labels should include producers at the base, primary consumers, secondary consumers, tertiary consumers, units where relevant, upright pyramid and inverted pyramid.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why is the pyramid of energy always upright?
Think first, then show answerHide answer
Common wrong answer
Drawing an inverted pyramid of energy is incorrect because energy cannot increase at higher trophic levels.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
Answer plan
- 1
Enough for 1 mark
An ecological pyramid is a graphical representation of the number, biomass or energy content of organisms at successive trophic levels in an ecosystem.
- 2
Add for 2 marks
Example: In a tree ecosystem, one large tree can support many insects, which may support several birds. This can produce an inverted pyramid of number even though the tree has large biomass.
- 3
Add for 3 marks
The base usually represents producers, followed by primary, secondary and tertiary consumers.
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