Ecology & Food Chains

Biodiversity is the range and variety of different species of organisms found on Earth, or in a particular ecosystem

A coral reef has very high biodiversity (thousands of species per hectare). An intensive wheat field has very low biodiversity (one main species, plus a few weeds).

Why biodiversity matters

• Stability: ecosystems with high biodiversity are more resilient. If one species is wiped out by disease, other species can fill the gap. In a low-biodiversity system, losing a single species can collapse the whole food web.
• Food security: most food crops are descended from wild varieties. Wild relatives still hold genetic diversity that crop breeders may need in future (e.g. resistance to new diseases).
• Medicine: many drugs were originally discovered in wild plants, fungi or animals. Aspirin came from willow bark; penicillin from a mould; many cancer drugs from rainforest plants.
• Climate: forests, oceans and peat bogs all absorb large amounts of CO₂. Reducing biodiversity (especially through deforestation) accelerates climate change.
• Cultural and recreational value: people enjoy seeing wildlife. Many livelihoods depend on tourism around biodiversity hotspots.

Many human activities reduce biodiversity (covered in topic 16: Human Impact on the Environment): deforestation, pollution, overfishing, climate change, and the introduction of invasive species.