The Living WorldTopic Summary
Topic Summary: Ecosystems Overview
Part of Ecosystems Overview — GCSE Geography
This topic summary covers Topic Summary: Ecosystems Overview within Ecosystems Overview for GCSE Geography. Revise Ecosystems Overview in The Living World for GCSE Geography with 15 exam-style questions and 16 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 16 of 16 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 16 of 16
Practice
15 questions
Recall
16 flashcards
Topic Summary: Ecosystems Overview
Key Terms
- Ecosystem: Community of biotic and abiotic components interacting
- Biotic: Living components (plants, animals, decomposers)
- Abiotic: Non-living components (temperature, rainfall, soil)
- Producer: Organism making its own food via photosynthesis (TL1)
- Consumer: Organism that eats other organisms (TL2, 3, 4)
- Decomposer: Breaks down dead matter; returns nutrients to soil
- Nutrient cycling: Continuous movement of nutrients: Biomass → Litter → Soil → Biomass
- Succession: Progressive change in ecosystem over time → climax community
- Biome: Large-scale ecosystem defined by climate and vegetation type
- Trophic cascade: Indirect effects through food web when one trophic level changes
Six Major Biomes
- Tropical rainforest: 0–5° N/S; >2,000 mm; 25–27°C all year
- Tropical savanna: 5–15° N/S; seasonal wet and dry
- Hot desert: 20–30° N/S; <250 mm; extreme temperatures
- Temperate deciduous: 40–60° N; 4 seasons; 600–1,500 mm
- Coniferous (boreal): 60–70° N; cold; needle-leaf trees
- Tundra: >70° N; permafrost; mosses and lichens only
- Biome drivers: Latitude, atmospheric pressure, ocean currents, distance from sea, altitude
Nutrient Cycling: Three Biomes
- TRF: Giant biomass, tiny litter, tiny soil — nutrients in living organisms; fast decomposition; infertile soil when cleared
- Hot desert: Tiny biomass, tiny litter, medium soil — slow decomposition; limiting factor is water not nutrients
- Temperate: Large biomass, large litter (autumn), medium soil — balanced; fertile soils; supports agriculture
- Key rule: Energy FLOWS (one direction, lost as heat); nutrients CYCLE (indefinitely, between three stores)
- 10% rule: Only 10% of energy transfers between trophic levels; rest lost as heat, waste, uneaten material
Must-Know Evidence
- Yellowstone wolves (1995): Reintroduced 14 wolves → elk behaviour changed → riverbank vegetation recovered → rivers narrowed and deepened (trophic cascade)
- Epping Forest: Oak → caterpillar → blue tit → sparrowhawk; removing oaks collapses food chain AND nutrient cycle
- Sand dune succession: Pioneer (sea rocket) → marram grass → grey dune → dune slack → climax (UK oak woodland)
- Misconceptions to avoid: "Energy cycles" (wrong — it flows); "tropical soil is fertile" (wrong — nutrients in biomass); "removing one species = minor effect" (wrong — trophic cascades)