A level Biology B · Edexcel 9BI0 · Topic 10A
Ecosystems and populations
Key points
- Key terms: population (one species in one area), community (all populations in an area), habitat, niche (the role of a species and the conditions it needs).
- Two species cannot occupy exactly the same niche for long: one outcompetes the other.
- Abiotic factors: light, temperature, water, pH, soil nutrients. Biotic factors: predation, competition (intraspecific and interspecific), disease.
- Predator–prey populations rise and fall in cycles, with the predator peak lagging behind the prey peak.
- Sampling: quadrats (random for comparing areas; transects for change along a gradient). Mobile animals are estimated by mark–release–recapture: population = .
- Mark–release–recapture assumes marks do not harm or fall off and there is no migration, birth or death between samples.
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An ecosystem is a community of organisms together with the non-living conditions they live in. Population sizes rise and fall because of factors in the environment, and measuring them fairly in the field is a key practical skill.
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