Ecologists use capture-recapture to estimate the number of field crickets in a large area of heathland.
They catch and harmlessly mark 72 field crickets before releasing them. After 20 minutes, they place traps at three distances from the release point.
| Distance from release point in m | Total number caught | Number carrying a mark |
|---|---|---|
| 5 | 18 | 9 |
| 15 | 20 | 6 |
| 25 | 22 | 2 |
Calculate the estimated population of field crickets using all the results from the second catch.
Explain how the pattern in the results could affect the accuracy of the population estimate.
109 exam-style questions on OCR GCSE Biology 6.1 Monitoring and maintaining the environment, covering 6.1.1 Field investigation of distribution and abundance, 6.1.2 Human interactions and biodiversity, 6.1.3 Maintaining biodiversity, and 6.1.4 Environmental change and distribution of organisms. Each one has a worked solution and a mark scheme showing where the marks go.