Levels of organisation in an ecosystem
Biologists describe life at nested scales: organism, population, community, ecosystem, biosphere. Each level contains all the levels below it.
Ecologists use a hierarchy of terms β each one bigger and broader than the last. Learn the definitions and the order because AQA examiners ask for them directly.
Organism. A single living thing. One robin in your garden is an organism. So is one oak tree, one earthworm, one bacterium.
Population. All the individuals of one species living in the same place at the same time. Every grey squirrel in Richmond Park is a population. Every bluebell in an English woodland is a different population.
Community. All the populations of all the different species living in the same place at the same time. A UK oak woodland community includes oak trees, bluebells, squirrels, deer, owls, fungi, bacteria, beetles and so on β all interacting.
Ecosystem. A community PLUS the non-living (abiotic) parts of the environment it interacts with β soil, water, sunlight, air, temperature. A pond, a hedgerow, a rocky shore and the Amazon rainforest are all ecosystems, just at different sizes.
Biosphere. Every single ecosystem on Earth added together β the thin layer of land, water and air where life exists. There is only one biosphere.
Why the hierarchy matters. When you answer an exam question, choose the right level. If the question asks about all the bluebells in a wood β that's a population. All the species in the wood β community. Wood + soil + climate β ecosystem.
Organism = one individual.
Population = all of one species in an area.
Community = all species in an area.
Ecosystem = community + non-living surroundings.
Biosphere = all ecosystems on Earth.