2.5 Zonation, succession and change in ecosystemsIB Environmental Systems and Societies SL: Subtopic test

1. 1
   On a rocky shore in south Devon, students lay a transect from the top of the shore, which is only wetted by the highest tides, down to the low-tide mark. Near the top they find lichens and small periwinkles. In the middle of the shore they find barnacles and limpets on the rock, with bladder wrack seaweed. At the bottom, which is uncovered only by the lowest tides, they find large kelp and a wide variety of red seaweeds. Time covered by the tide, wave exposure and temperature changes are different at each level.

   (a)

   The change in the community from the top to the bottom of the rocky shore is an example of:

   [1 mark]

   • APrimary succession
   • BZonation
   • CA food chain
   • DBioaccumulation

   (b)

   Which abiotic factor changes along the transect and is most likely to explain the zones?

   [1 mark]

   • AThe mass of the transect rope
   • BThe pH of the rain
   • CThe number of students sampling
   • DThe length of time each level is exposed to air, which affects drying and temperature

   (c)

   Suggest why kelp is found only at the bottom of the shore, while barnacles live in the middle.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Surtsey is a volcanic island off the south coast of Iceland formed by eruptions between 1963 and 1967. The new island was bare lava and ash with no soil. The first vascular plant, sea rocket (Cakile arctica), was found in 1965 on the sand along the shore, and mosses and lichens became established on the lava later. A colony of gulls began nesting in the 1980s, and by 2008 about 70 species of vascular plant had been recorded on the island.

   (a)

   Which type of succession took place on Surtsey?

   [1 mark]

   • ASecondary succession, because the island had soil
   • BPrimary succession, because it began on newly formed land with no soil
   • CZonation
   • DClimax succession

   (b)

   Why are lichens and mosses important in the early stages of the succession?

   [1 mark]

   • AThey break down the rock and add organic matter, helping to form soil
   • BThey are the climax community
   • CThey remove competition from tall trees
   • DThey stop all other species from colonising

   (c)

   Explain how the colony of gulls affected the succession on Surtsey.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A conservation group followed the recovery of an abandoned pasture in northern England once grazing stopped. The first year had bare soil with 8 species of annual weeds and a soil depth of 5 cm. By year 10 there were perennial grasses and shrubs, 22 plant species and 12 cm of soil. By year 50 there was young birch and oak woodland with 35 plant species and 30 cm of soil. In the mature oak woodland at about year 150, there were 28 plant species (shaded out by large trees) and 45 cm of soil.

   (a)

   Calculate the percentage increase in the number of plant species between year 1 and year 50, and state one other change that took place as the succession progressed.

   [3 marks]

   (b)

   Explain why soil depth and plant species diversity increase during succession.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In May 1980 the eruption of Mount St Helens in Washington State, USA, flattened forest over about 600 km². Some areas were buried under deep pumice and ash, or swept by scalding flows, leaving no living organisms. In other areas, plants and soil under deep snow or on sheltered ground survived. In the years that followed, pioneer plants such as prairie lupin colonised the pumice, and animals such as pocket gophers brought buried soil to the surface. Decades later, some areas have recovered much more quickly than others.

   (a)

   Using the Mount St Helens eruption, explain the difference between primary and secondary succession and describe how a community develops in each.

   [6 marks]

   (b)

   To what extent does the diversity of an ecosystem determine its ability to tolerate a disturbance such as the eruption?

   [6 marks]

   Total for question 4: 12 marks

End of questions