Edexcel IGCSE Biology · Spec 4.1
Ecology Key Terms
Key ecology terms you need to know — population, community, habitat and ecosystem.
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Ecology Key Terms
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Explained
The ecology vocabulary, arranged from smallest to largest
These words are used loosely in ordinary speech and precisely in biology, and questions test the precise meanings. Learning them in size order makes the differences obvious, because each one contains the one before it.
The four terms
A habitat is the place where an organism lives. A rock pool, an oak tree, the bank of a stream.
A population is all the individuals of one species living in an area at one time. All the limpets in the rock pool.
A community is all the populations of all the different species living in an area. Every limpet, every crab, every seaweed and every barnacle in that pool, together.
An ecosystem is the community plus the non living parts of the environment it interacts with. The community in the rock pool, plus the water, the rock, the temperature, the salinity and the light.
So the chain runs population, then community, then ecosystem, each one larger than the last. The only word outside that sequence is habitat, which describes a place rather than a collection of organisms.
Biotic and abiotic
Biotic factors are the living parts of an environment: predators, prey, competitors, disease, food supply.
Abiotic factors are the non living parts: temperature, light intensity, water, pH, oxygen concentration, wind, soil type.
The distinction is what turns a community into an ecosystem. A community is biotic only; add the abiotic factors and you have the ecosystem.
Take care with a few borderline cases. Dead leaves and faeces came from living things but are not themselves alive, so they are usually treated as abiotic. Competition is biotic; drought is abiotic; a shortage of food caused by drought involves both.
What the mark scheme accepts and rejects
An Edexcel International GCSE Biology mark scheme sets these definitions as one mark questions, and the wording it credits is worth reading closely.
For community it accepts all of the organisms of all species in an area, or all organisms in an area, or all species in an area. It allows different species, and it allows habitat in place of area.
For population it accepts all of one species, or a species in an area, and again allows habitat or ecosystem for area.
Set those two lists side by side and the entire distinction is one phrase. All species, or one species. Everything else in both answers is identical, which is why an answer that says all the organisms living in an area could be describing either, and why the mark depends on a word that is easy to leave out.
Notice also how flexible the mark schemes are about area, habitat and ecosystem here, while being rigid about the species clause. That is the pattern across biology: the setting can be described loosely, and the biology cannot.
Using them together
Questions often give a scenario and ask you to identify which term applies, so practise running one example through all four.
An oak woodland is the habitat. All the grey squirrels in it are a population. The squirrels together with the oaks, the beetles, the fungi, the owls and everything else form the community. That community plus the soil, the rainfall, the temperature and the light forms the ecosystem.
The commonest error is using population where community is meant. If more than one species is involved, the word is community.
Two more terms that follow on
A niche is the role an organism plays in its ecosystem: what it eats, what eats it, when it is active, where in the habitat it lives. Two species with identical niches cannot coexist for long, because one will outcompete the other.
Biodiversity is the variety of living organisms in an ecosystem, counted both as the number of different species and as the abundance of each. A wood with ten species is more biodiverse than one with three, and one where those ten species are evenly represented is more biodiverse than one dominated by a single species.
Spec 4.1
What you need to know
- Define population and community
- Define habitat and ecosystem
- Use the terms together in an example
Active recall
Quick check
Answer each question before opening the answer.
Define population, community and ecosystem.
Population — all the members of one species in an area. Community — all the populations living together. Ecosystem — the community plus its non-living (abiotic) environment.
What is a habitat?
The place where an organism lives.
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