Knowledge Organiser: 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)
Common Mistakes
- Saying energy cycles: Energy flows in one direction and is lost as heat — only nutrients cycle between biomass, litter and soil
- Confusing producers and consumers: Producers make their own food via photosynthesis; consumers eat other organisms — always state the trophic level
- Describing biomes without naming one: Exam answers must name a specific biome (e.g. tropical rainforest, hot desert) with a located example
- Stating "one species doesn't matter": Trophic cascades show a single species change (e.g. wolves at Yellowstone) can transform an entire ecosystem
Memory Aid
- B — Biotic (living: plants, animals, fungi, bacteria, decomposers)
- L — Links (food webs, energy flow, feeding relationships)
- E — Energy (flows in one direction; 10% passes between trophic levels)
- N — Nutrient cycling (three stores: Biomass, Litter, Soil)
- D — Distribution (biomes: controlled by latitude, precipitation, ocean currents, altitude)
- Latitude (distance from equator → controls temperature)
- Atmospheric pressure belts (rising air at equator = rain; descending air at 25–30° = desert)
- Ocean currents (Gulf Stream warms NW Europe; cold currents create fog deserts)
- Distance from sea / continentality (coasts = moderate; interiors = extreme)
- Altitude (temperature falls 6.5°C per 1,000 m)