Key Idea: Most marks in topic 2.5 come from how an ecosystem changes during succession, and from zonation. Learn those first.
1. Changes during succession (most marks)
- Soil gets deeper and holds more water and nutrients.
- Species diversity and biomass increase.
- Food webs become more complex, and nutrient cycling speeds up.
- The community becomes more stable and resilient.
2. Succession
- Succession: one community replaces another over time.
- Each sere changes conditions so the next can move in.
- Primary: new ground with no soil, such as lava. Secondary: soil left, such as after a fire.
- Pioneers (lichens, mosses) start it; the climax community ends it.
3. Zonation
- Zonation: communities change along an environmental gradient, in space.
- Examples: up a mountain, or down a rocky shore.
- Measure it with a transect and show it on a kite diagram.
- Succession is change over time; zonation is change over space.
How it is examined:
| Question | How to score |
|---|---|
| [1] Identify a zone or vegetation type from a figure | Read the figure; copy the name exactly. |
| [2] Outline why vegetation changes with altitude | Name the abiotic factor (temperature) and its effect. |
| [2] to [3] Describe the stages of a succession | Pioneers, then soil builds, then taller plants, then climax. |
| [4] Outline how a climax differs from a pioneer community | Diversity, biomass, soil depth, stability: one each. |
| [7] Explain how succession changes an ecosystem | Soil, diversity, productivity, nutrient cycling, resilience, with a named example. |
Key terms, one line each:
| Term | In one line |
|---|---|
| Zonation | the change in community along an environmental gradient |
| Succession | the replacement of one community by another over time |
| Sere | one stage in a succession |
| Pioneer species | the first organisms to colonise bare ground, such as lichens |
| Climax community | the stable community at the end of a succession |
| Resilience | the ability of an ecosystem to recover after a disturbance |
Last-minute check: answer, then tap to see.
What is the difference between zonation and succession? Zonation is change over space; succession is change over time.
Why can lichens live on bare rock? They need no soil and start to weather the rock.
Is succession after a forest fire primary or secondary? Secondary: the soil is still there.
What happens to soil depth during succession? It increases, as dead matter builds up.
Why is a climax community more stable? More species and more complex food webs, so it recovers better.
Surtsey, an island off Iceland, rose from the sea in a volcanic eruption in 1963. Outline four ways the ecosystem on Surtsey changes as succession takes place.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Exam tips
- Say what changes AND in which direction: soil gets deeper, diversity increases.
- Zonation is space, succession is time: never mix them up.
- Name a real example: Surtsey, Mount St Helens, a glacier foreland.
- For primary or secondary, ask one question: is there soil already?