CB9.1 — Ecosystems (Edexcel 1SC0)
📖Definition— Key terms
- Ecosystem: all the living organisms in an area plus the non-living environment.
- Biotic factors: living factors (predators, prey, competitors, pathogens, pollinators).
- Abiotic factors: non-living factors (temperature, pH, light, water, soil mineral content, salinity).
- Population: all organisms of the same species in an area.
- Community: all the populations in an area.
Interdependence
Species in an ecosystem are interdependent:
- Food chains / food webs: energy transfer between organisms.
- Removing one species can affect the whole ecosystem (e.g. removing a predator → prey population explodes).
Sampling techniques
Quadrats: 1 m² squares placed randomly in a habitat. Count organisms or estimate percentage coverage.
- Frequency: presence/absence in the quadrat.
- Percentage cover: estimate of area covered by a species.
Transects: a line (or belt transect) across a habitat; quadrats placed at intervals. Used to study the distribution of organisms across a gradient (e.g. from low to high tide on a seashore).
Capturing animals: pitfall traps; sweep nets; mark-release-recapture (Lincoln Index).
$$N = \frac{n_1 \times n_2}{m}$$
Where: N = population size; n₁ = first sample; n₂ = second sample; m = marked animals in second sample.
Biodiversity
Biodiversity = variety of species and their relative abundance. Measured by species richness or a biodiversity index.
Higher biodiversity → more stable ecosystem.
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