Cambridge O Level Biology · Syllabus 5090 · Relationships of Organisms with One Another and with the Environment
Population Estimate
What is Population Estimate?
A calculated approximation of the number of organisms in a study area, obtained by finding the mean number counted per quadrat and scaling that mean up by the number of quadrat areas that fit into the whole study area. It is an estimate rather than a count, because only a small fraction of the area is examined and the calculation assumes the sampled quadrats are representative of the whole. Increasing the number of quadrats sampled generally improves reliability but never turns the estimate into an exact figure.
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 Population Estimate
- “A population estimate is the number of organisms present.” Why it is wrong: only a small fraction of the area was examined, and the calculation assumes those samples represent the whole. Exam-safe: it is an estimate. State that the organisms may not be evenly distributed and that more quadrats would improve reliability.
Questions students ask about Population Estimate
Is a population estimate the same as a count?
No. Only a small fraction of the study area is examined, and the calculation assumes those quadrats represent the whole. Always call it an estimate, and be ready to give a limitation: the small proportion sampled, or the possibility that the organisms are not evenly distributed.