A group of ecology students investigated the population density of freshwater limpets (Ancylus fluviatilis) in a shallow stream over a 12-week period following a seasonal drought.
To monitor the community, they placed a 0.25 m2 quadrat at four specific sampling sites (Sites 1 to 4) along the stream bed. Every three weeks, they counted the number of limpets within each quadrat before returning them carefully to their microhabitats.
Table 1 shows their findings.
Table 1: Number of freshwater limpets in each quadrat sample
| Sampling site | 0 weeks | 3 weeks | 6 weeks | 9 weeks | 12 weeks |
|---|---|---|---|---|---|
| 1 | 32 | 26 | 19 | 11 | 5 |
| 2 | 26 | 21 | 15 | 9 | 4 |
| 3 | 38 | 31 | YYY | 15 | 6 |
| 4 | 24 | 18 | 14 | 7 | 3 |
| Totals | 120 | 96 | 72 | 42 | 18 |
Value Y Y\,Y represents the number of limpets recorded at sampling site 3 at 6 weeks. Calculate the value of YYY.
Calculate the percentage decrease in the total number of freshwater limpets recorded at 9 weeks compared with 0 weeks.
63 exam-style questions on AQA GCSE Biology 7.1 Adaptations, interdependence and competition, covering 7.1.1 Communities, 7.1.2 Abiotic factors, 7.1.3 Biotic factors, and 7.1.4 Adaptations. Each one has a worked solution and a mark scheme showing where the marks go.