Ecology and human influences on ecosystems

Energy flow

Food chains and webs; producers, consumers and decomposers; trophic levels; pyramids of numbers, biomass and energy. Energy is lost at each level (respiration, heat, waste), so food chains are short.

Nutrient cycles

Carbon cycle (photosynthesis, respiration, combustion, decomposition, fossilisation); nitrogen cycle (nitrogen fixation, decomposition, nitrification, denitrification) and the role of bacteria.

Populations

Factors affecting population size (food, predation, disease, competition); sigmoid growth curves; the human population and its effects.

Human influences

• Food supply: monocultures, fertilisers, pesticides, intensive livestock.
• Habitat destruction: deforestation, land clearance, mining.
• Pollution: eutrophication from fertilisers and sewage; non-biodegradable plastics; acid rain; greenhouse gases and climate change.
• Conservation: protected areas, sustainable forestry and fishing, seed banks, captive breeding, education and international agreements (e.g. CITES).

Check yourself

1. Why are food chains rarely longer than five trophic levels?
2. Name the bacteria that convert ammonium compounds to nitrates.
3. Give two reasons for conserving forests.