Human impact and conservation

Human pressures on biodiversity

A growing population needs land, food, energy and resources. Four pressures dominate OCR questions:

1. Pollution — air (SO₂, NOx, particulates), water (sewage, fertiliser run-off → eutrophication), land (plastics, pesticides).
2. Deforestation — clearing for agriculture, biofuels and timber. Removes habitat, reduces CO₂ uptake, increases soil erosion.
3. Peat-bog destruction — peat decomposes when drained for fuel/compost, releasing stored CO₂.
4. Climate change — rising global temperatures, melting ice, shifting habitats; species that cannot migrate or adapt face extinction.

Indicators of pollution

Living indicator species can show air or water quality:

• Lichens — sensitive to SO₂ in air. Many species → clean air; few or none → polluted.
• Mayfly larvae / freshwater shrimp — need high dissolved O₂. Their absence indicates organic pollution.
• Bloodworms / sludge worms — tolerate low O₂; their dominance signals heavy pollution.

Chemical/electronic methods (e.g. dissolved O₂ probes, pH meters) are quicker and quantitative; biological indicators are cheaper, integrate over time and need no power.

Conservation programmes

OCR expects you to know specific actions:

• Captive breeding in zoos (e.g. Arabian oryx) → reintroduction.
• Seed banks preserve plant biodiversity.
• Protected areas / SSSIs / national parks safeguard habitat.
• Reforestation restores carbon sinks and habitats.
• Quota systems limit fish catches.
• Education and ecotourism fund conservation and shift incentives.

Maintaining biodiversity = ecosystem stability

Diverse ecosystems are more stable: more species → more redundancy in food webs → ecosystem services (pollination, decomposition, climate regulation) keep working when one species declines.

OCR exam tip

When asked "evaluate" a measure, give a benefit and a limitation. e.g. "Captive breeding can reintroduce species (benefit), but reduces genetic diversity if the founder population is small (limit)."