1. 1
   Surtsey is a volcanic island that rose from the sea off Iceland between 1963 and 1967, leaving bare lava and ash with no soil. Mosses and lichens colonised the lava, and the first flowering plant, sea rocket (Cakile maritima), was recorded in 1965 from seeds carried by the sea. By 1985 about 20 species of vascular plant had been recorded. In 1986 a breeding colony of gulls became established on one part of the island. The number of plant species then rose rapidly, mostly inside the gull colony, reaching 69 species by 2008. Soils inside the colony are now deeper and much richer in nitrogen and phosphorus than elsewhere on the island.

   (a)

   Which change is expected as primary succession continues on Surtsey?

   [1 mark]

   • AAn increase in the amount of nutrient cycling
   • BA decrease in the complexity of food webs
   • CA decrease in the size of the plants
   • DA decrease in primary production

   (b)

   What caused the rapid increase in plant species after 1986?

   [1 mark]

   • AA change in an abiotic factor caused by renewed volcanic eruption
   • BA change in a biotic factor, as gulls enriched the soil with nutrients
   • CArrested succession caused by grazing animals
   • DCyclical succession returning the island to bare lava

   (c)

   Explain why the number of plant species increased more quickly inside the gull colony than elsewhere on the island.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On a hillside in northern England, sheep have grazed an area of grassland for several centuries. Twenty years ago, ecologists fenced off several plots so that sheep could not enter them, and left other plots open to grazing. The open plots are still short grassland. The fenced plots now contain dense scrub and young birch and rowan trees up to 5 m tall. In the same region, a large area of lowland fen was drained with ditches in the nineteenth century and has been used as farmland ever since; where small areas of fen were never drained, they have developed into wet woodland dominated by alder and willow.

   (a)

   What do the results from the fenced and grazed plots indicate?

   [1 mark]

   • AFencing triggered primary succession on bare rock
   • BThe climax community in this area is short grassland
   • CGrazing by sheep has arrested succession, preventing development of the woodland climax community
   • DBirch and rowan cannot grow in this climate

   (b)

   Which change would be expected in the fenced plots over the 20 years?

   [1 mark]

   • AA return to bare ground
   • BA decrease in primary production
   • CLoss of all soil nutrients
   • DAn increase in the height and biomass of the tallest plants

   (c)

   Explain how drainage of the fen prevented the climax community from developing.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   On heather moorland in Scotland, patches of heather (Calluna vulgaris) pass through four phases. In the pioneer phase (0–6 years), young heather seedlings establish on bare ground and cover about 10% of the ground. In the building phase (6–15 years), heather forms a dense canopy covering about 90% of the ground. In the mature phase (15–25 years), the canopy begins to thin, with about 75% cover. In the degenerate phase (over 25 years), the old central stems collapse, leaving a gap with about 25% heather cover and much bare ground, lichen and moss. The mean number of other plant species per patch was 12 in the pioneer phase, 3 in the building phase, 5 in the mature phase and 14 in the degenerate phase. Heather seedlings then establish in the gap and the pioneer phase begins again.

   (a)

   Explain why this is described as cyclical succession rather than succession to a single climax community.

   [3 marks]

   (b)

   Analyse the changes in the number of other plant species through the four phases.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A class set up twelve sealed glass jars, each containing 500 cm³ of pond water, 50 g of pond sediment, two shoots of the pondweed Elodea and two water snails. Six jars were placed by a sunny window and six in a dark cupboard, all at 20 °C. Dissolved oxygen was measured weekly with a probe inserted through a sealed port in the lid. In the jars in light, dissolved oxygen stayed between 7.5 and 8.5 mg dm⁻³ for 10 weeks, and the snails survived and laid eggs. In the jars in the dark, dissolved oxygen fell to 1.0 mg dm⁻³ by week 3, the snails had died by week 4 and the Elodea decayed.

   (a)

   Explain the results with reference to the requirements for stability in ecosystems.

   [6 marks]

   (b)

   Evaluate the use of these jars as a model for investigating the stability of natural ecosystems.

   [6 marks]

   Total for question 4: 12 marks

End of questions