Key Terms

📖 Key Terms

ecosystem — A community of living organisms (biotic factors) interacting with each other and with their non-living environment (abiotic factors). Ecosystems exist at all scales, from a rock pool to the entire Amazon basin.

biotic factors — The living components of an ecosystem: all plants, animals, fungi, bacteria, and other organisms. They interact with each other through feeding, competition, and decomposition.

abiotic factors — The non-living physical and chemical components of an ecosystem: temperature, rainfall, sunlight, soil type, geology, topography, pH, and wind. They shape which organisms can survive in a place.

producer — An organism (usually a green plant) that manufactures its own food through photosynthesis, converting solar energy into chemical energy stored in biomass. Producers are trophic level 1 and the foundation of all food chains.

consumer — An organism that obtains energy by eating other organisms. Primary consumers (herbivores) eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers.

decomposer — An organism (bacteria or fungi) that breaks down dead organic matter, releasing nutrients back into the soil. Decomposers complete the nutrient cycle and without them nutrients would remain locked in dead organic matter permanently.

food web — A diagram showing all the feeding relationships in an ecosystem simultaneously — multiple interconnected food chains. Food webs are more realistic than food chains because most organisms eat and are eaten by more than one species.

trophic level — The position an organism occupies in a food chain. Level 1 = producers; Level 2 = primary consumers; Level 3 = secondary consumers; Level 4 = tertiary consumers (apex predators).

nutrient cycling — The continuous movement of chemical nutrients (nitrogen, phosphorus, carbon, etc.) between the three stores of biomass, litter, and soil. Unlike energy, nutrients are cycled indefinitely — they are not lost from the ecosystem.

biomass — The total mass of living organic material in an ecosystem or at a particular trophic level. In tropical rainforests, the biomass store is enormous and holds most of the ecosystem's nutrients.

succession — The progressive change in an ecosystem over time, as organisms colonise bare ground, modify abiotic conditions, and enable more complex communities to establish. Ends at the climax community for that climate.

biome — A large-scale ecosystem, covering a vast area, defined by its climate and characterised by a distinctive type of vegetation and associated fauna. Examples include tropical rainforest, hot desert, temperate deciduous forest, and tundra.

trophic cascade — The indirect effect that a change at one trophic level has on lower (or higher) trophic levels. The Yellowstone wolf reintroduction is the classic example: wolves affected elk behaviour, which affected vegetation, which affected river morphology.