Cambridge O Level Biology · Syllabus 5090 · Relationships of Organisms with One Another and with the Environment
Pyramid of Numbers
What is Pyramid of Numbers?
A diagram in which the width of each bar represents the number of organisms at that trophic level, with the producer placed at the base and each successive level stacked above it. The bars have equal height and share a common central axis. Because bar width counts individuals and takes no account of their size, a pyramid of numbers can be inverted: a single large producer such as an oak tree may support thousands of small primary consumers, giving a narrow base and a much wider second level.
This definition is part of the Relationships of Organisms with One Another and with the Environment chapter in Cambridge O Level Biology.
Common mistakes with Pyramid of Numbers
- “A pyramid of numbers is always upright.” Why it is wrong: bar width counts individuals regardless of size, so one large producer can support many small consumers. Exam-safe: a pyramid of numbers may be inverted, for example when a single oak tree supports thousands of caterpillars.
Questions students ask about Pyramid of Numbers
Can a pyramid of numbers really be upside down?
Yes. Bar width counts individuals and takes no account of size, so a single large producer such as an oak tree can support thousands of caterpillars, giving a narrow base and a much wider second level. Parasites do the same thing higher up a chain. A pyramid of energy, by contrast, is always upright when correctly constructed.