How do ecosystems function and change over time?
Ecosystem structure, energy flow and nutrient cycling, succession to a climax community, and the management of fragile ecosystems.
A focused CCEA A-Level Geography answer on ecosystems, covering ecosystem structure, energy flow through trophic levels, nutrient cycling, succession to a climatic climax, and the management of fragile ecosystems using located Northern Ireland examples such as the Murlough sand dunes and Garron Plateau blanket bog.
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What this dot point is asking
CCEA wants you to describe ecosystem structure, explain energy flow and nutrient cycling, account for succession from a pioneer community to a climatic climax, and evaluate the management of a fragile ecosystem, using located examples such as the Murlough sand dunes and the Garron Plateau blanket bog in County Antrim.
Ecosystem structure and energy flow
An ecosystem has living (biotic) and non-living (abiotic) components linked by flows of energy and matter. Energy enters as sunlight and is fixed by producers through photosynthesis, then passes to primary, secondary and tertiary consumers, with decomposers (bacteria and fungi) breaking down dead matter and releasing nutrients. The amount of living material at each level is shown by a pyramid of biomass, which narrows sharply upward.
Nutrient cycling
In a temperate ecosystem, transfers slow in winter, so the litter store accumulates; in tropical rainforest, rapid year-round decomposition means most nutrients are held in the biomass and recycling is fast, which is why cleared rainforest soils lose fertility quickly. On Northern Ireland's blanket bogs, waterlogged, acidic, anaerobic conditions slow decomposition almost completely, so dead matter accumulates as peat rather than cycling back, locking up carbon.
Succession
Succession is the directional change in a community over time. A primary succession begins on a bare surface with a pioneer community; each seral stage modifies the environment (adding humus, retaining moisture, lowering pH), allowing more demanding species to colonise until a stable climatic climax is reached. Where human activity such as grazing or burning halts succession, a plagioclimax develops, for example the heather moorland of the Antrim uplands maintained by sheep grazing and managed burning.
Managing fragile ecosystems
The Garron Plateau is the largest intact blanket bog in Northern Ireland and a key carbon and water store. Restoration here (blocking old drainage ditches to re-wet the peat) shows management aimed at carbon storage and water quality for Belfast's supply, a contrast with the recreation-led management at Murlough.
Examples in context
Example 1. Murlough psammosere, County Down. Sediment supplied by longshore drift in Dundrum Bay built a 6,000-year-old dune system. Marram grass pioneers stabilise mobile sand; as humus builds, fixed grey dunes support a rich sward, then dune slacks and scrub. The reserve illustrates both primary succession and conservation management under heavy recreational pressure, with grazing used to prevent scrub from shading out rare dune species.
Example 2. Garron Plateau blanket bog (carbon and water management). This Special Area of Conservation stores vast amounts of carbon in waterlogged peat where anaerobic conditions halt decomposition. Past drainage and overgrazing dried and eroded the bog; a restoration partnership has blocked ditches and reduced grazing to re-wet the peat, restoring its function as a carbon sink and improving raw-water quality for the catchment. It shows fragile-ecosystem management driven by climate and water goals rather than tourism.
Try this
Q1. Name the three nutrient stores in the Gersmehl model. [2 marks]
- Cue. Biomass, litter and soil.
Q2. Explain why energy is lost between trophic levels in a food chain. [3 marks]
- Cue. Most energy is used in respiration and lost as heat, with further losses in egestion, so only around passes to the next level.
Q3. With reference to a located example, evaluate the management of a fragile ecosystem. [6 marks]
- Cue. Murlough dunes or Garron Plateau bog; balance conservation, recreation, grazing, carbon and water; reach a judgement on effectiveness.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20194 marksExplain how nutrients are cycled within an ecosystem with reference to the Gersmehl model.Show worked answer →
Worth 4 marks. Markers reward naming the three stores, the transfers between them, and the inputs and outputs, ideally contrasting two biomes.
Stores: biomass (living matter), litter (dead organic material on the surface) and soil. These are drawn proportional to the nutrients held.
Transfers: fallout from biomass to litter (leaf fall), decomposition from litter to soil, and uptake from soil to biomass. Inputs come from weathering of parent rock and from precipitation; outputs are leaching and surface runoff.
Contrast: in tropical rainforest the biomass store dominates and recycling is fast; in temperate woodland slower winter decomposition lets the litter store build up.
CCEA 20227 marksWith reference to a located example, describe the stages of succession and explain how a fragile ecosystem is managed.Show worked answer →
Worth 7 marks. Reward an ordered seral sequence plus evaluated management of a named site.
Succession: at Murlough a psammosere develops. Pioneers such as sand couch and marram grass colonise embryo and foredunes, trapping sand and adding humus; this allows yellow then fixed grey dunes with greater diversity, then dune slacks and scrub, tending toward a climax woodland.
Management: as a National Nature Reserve run by the National Trust, the dunes face heavy visitor and grazing pressure. Boardwalks concentrate footfall, fencing protects fragile foredunes, and controlled grazing maintains the grey-dune sward.
Judgement: management is largely effective in balancing conservation with recreation, though climate change and storm erosion remain pressures.
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Sources & how we know this
- CCEA GCE Geography specification — CCEA (2016)