Explaining Change: Ecosystems and Biodiversity — AQA Combined Science: Synergy
This topic covers levels of organisation in ecosystems, interdependence, the factors affecting communities, biodiversity and human impacts.
Levels of organisation
- Population — all the organisms of one species in a habitat.
- Community — all the populations of different species.
- Ecosystem — the community plus the non-living (abiotic) environment.
Organisms compete for resources: plants for light, space, water and minerals; animals for food, mates and territory.
Interdependence and competition
Species depend on each other for food, shelter, pollination and seed dispersal — interdependence. In a stable community the species and environment are in balance so populations stay roughly constant. In a food web, predator and prey populations rise and fall in cycles.
Factors that affect communities
Abiotic (non-living): light intensity, temperature, moisture, soil pH and minerals, wind, CO₂ and oxygen levels. Biotic (living): availability of food, new predators, new pathogens and competition.
Organisms have structural, behavioural and functional adaptations to survive their conditions. Extremophiles live in extreme conditions.
Field investigations
Required practical: measuring the distribution and abundance of organisms using quadrats (for abundance, sampling randomly) and transects (to study how distribution changes across an area). You should be able to calculate means and estimate population sizes from samples.
Biodiversity
Biodiversity is the variety of species in an ecosystem or on Earth. High biodiversity makes ecosystems more stable. The future of humans depends on maintaining biodiversity.
Negative human impacts on ecosystems
A growing population and higher living standards use more resources and produce more waste:
- Pollution of water, air and land.
- Land use for building, farming, quarrying and waste.
- Deforestation — reduces biodiversity and removes carbon stores.
- Peat bog destruction — releases CO₂ and destroys habitats.
- Global warming from greenhouse gases.
Positive human impacts
Conservation actions include breeding programmes for endangered species, protecting and regenerating habitats, replanting hedgerows and field margins, reducing deforestation and recycling waste. These often involve a conflict between human needs and conservation.
Exam tips
- Distinguish abiotic and biotic factors with examples.
- Explain predator–prey cycles using food availability.
- For quadrat questions, calculate means and estimate total populations from samples.
- Give balanced positive and negative human impacts on biodiversity.