Question 1
Paper 2Medium16 marksA coastal reserve contains upper sand dunes beside a mangrove swamp. Researchers placed ten randomly positioned 1 m² quadrats at each of four sites. The table shows the mean number of living shoots of marram grass (Ammophila arenaria) and seedlings of the mangrove tree Avicennia marina per quadrat.
| Site | Habitat | Soil salinity / g kg⁻¹ | Soil water content / % | Marram shoots per quadrat | A. marina seedlings per quadrat |
|---|---|---|---|---|---|
| A | Upper dune | 2 | 4 | 13 | 0 |
| B | Dune–swamp boundary | 14 | 18 | 6 | 4 |
| C | Inner mangrove swamp | 28 | 42 | 0 | 16 |
| D | Creek edge | 36 | 55 | 0 | 8 |
Field notes describe the following features: marram leaves roll inward in dry air, enclosing the stomata in a humid space, and its roots spread widely through loose, shifting sand. A. marina has upright pneumatophores that project above the waterlogged sediment, and salt glands on its leaves release salt.
To estimate the number of marram shoots in an 800 m² upper-dune patch, researchers counted the shoots in ten additional randomly placed 1 m² quadrats. The counts were 12, 15, 9, 14, 16, 11, 13, 10, 17 and 13.
Researchers also surveyed an estuarine snail in five pools of similar area, counting snails in 10 m² at each pool. The same search time was used at each pool, and other measured conditions were similar.
| Water temperature / °C | Snails counted per 10 m² |
|---|---|
| 14 | 1 |
| 18 | 7 |
| 22 | 15 |
| 26 | 8 |
| 30 | 0 |
State one abiotic variable measured in the plant survey and one measured in the snail survey.
Describe how the abundance of the two plant species changes across the sites as soil salinity increases.
Estimate the number of marram shoots in the 800 m² upper-dune patch.
Explain how the features described in the field notes may help marram and A. marina live in their respective habitats.
Describe the pattern in the snail counts, including the observed temperature range of pools in which snails were recorded.
A student concludes that soil salinity alone determines which of the two plant species occurs at each site. Evaluate this conclusion, using the plant data and field notes.