Ecology
Ecosystems, interdependence, biodiversity, and human impact.
In this topic
Ecosystems and Communities
An ecosystem is the interaction of a community of living organisms (biotic factors) with the non-living parts of their environment (abiotic factors).
Key terms: - Habitat: where an organism lives - Population: all organisms of one species in a habitat - Community: all the populations in a habitat - Abiotic factors: temperature, light, water, soil pH, wind - Biotic factors: predation, competition, disease, food availability
Organisms in a community depend on each other — this is interdependence. If one species is removed, it can affect the whole food web.
Key Points
- Abiotic = non-living factors; Biotic = living factors
- Competition can be interspecific (between species) or intraspecific (within a species)
- Organisms compete for: food, water, space, mates, light (plants)
- Predator-prey cycles are linked — as prey increases, predators increase, then prey decreases
Example Questions
4Explain what might happen to a food web if a key herbivore species was removed.
The plants it ate would increase in number due to less grazing. Predators that ate the herbivore would decrease due to less food. Other herbivores might increase due to less competition. This could have knock-on effects throughout the food web.
[4 marks]
Biodiversity and Human Impact
Biodiversity is the variety of all living organisms on Earth. High biodiversity makes ecosystems more stable and resilient.
Human activities reducing biodiversity: - Deforestation: habitat loss, less CO₂ absorption, soil erosion - Pollution: air (CO₂, SO₂), water (sewage, fertilisers), land (landfill, toxic waste) - Global warming: rising temperatures change habitats, ice caps melt, extreme weather - Overfishing and hunting
Conservation methods: - Breeding programmes for endangered species - Habitat protection and nature reserves - Seed banks to preserve plant genetic material - Reducing deforestation and replanting
Key Points
- Biodiversity is essential for ecosystem stability
- Global warming is primarily caused by increased greenhouse gases
- Eutrophication: excess fertiliser → algal bloom → oxygen depletion → death
- Sustainability means meeting current needs without compromising future generations
Example Questions
4Explain how the use of fertilisers can lead to the death of fish in rivers.
Excess fertiliser runs off into rivers (eutrophication). This causes rapid growth of algae (algal bloom). The algae block light, causing plants beneath to die. Bacteria decompose the dead plants, using up oxygen. Fish and other aquatic organisms die due to lack of oxygen.
[4 marks]