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Global biodiversity is declining at an unprecedented rate. The Living Planet Index estimates that monitored wildlife populations have fallen by around 69% since 1970, and the IUCN Red List identifies tens of thousands of species as threatened with extinction. Understanding why biodiversity is declining is essential both for exam success and for making informed conservation decisions. OCR A-Level Biology A specification 4.2.1 (g) requires you to explain how human activities affect biodiversity and to evaluate the importance of conserving it.
Key Definitions:
- Anthropogenic — caused or produced by human activity.
- Deforestation — large-scale removal of forest cover.
- Monoculture — cultivation of a single crop species over a large area.
- Eutrophication — nutrient enrichment of water, often leading to algal blooms.
- Climate change — long-term shifts in global weather patterns caused primarily by greenhouse gas emissions.
flowchart TD
A[Biodiversity Loss] --> B[Habitat Destruction]
A --> C[Climate Change]
A --> D[Pollution]
A --> E[Overexploitation]
A --> F[Invasive Species]
B --> B1[Deforestation]
B --> B2[Agricultural expansion]
B --> B3[Urbanisation]
D --> D1[Pesticides]
D --> D2[Eutrophication]
D --> D3[Plastic]
Conservation biologists sometimes use the acronym HIPPO to remember the main drivers: Habitat loss, Invasive species, Pollution, Population (human), and Overharvesting. OCR focuses on three in particular: deforestation, agriculture and climate change.
Forests hold around 80% of the world's terrestrial biodiversity, with tropical rainforests especially rich — the Amazon alone is home to at least 40,000 plant species, 2,500 fish, 1,300 birds and millions of invertebrates. Each year, approximately 10 million hectares of forest are cleared worldwide, mainly for:
Palm oil plantations in Borneo and Sumatra have destroyed more than half of orangutan habitat since the 1990s. Population estimates for Bornean orangutans have fallen from over 230,000 in the 1970s to around 100,000 today; the Sumatran and Tapanuli species are critically endangered.
Agriculture now occupies around half of the world's habitable land. While it feeds us, it also represents the single biggest driver of terrestrial biodiversity loss. Intensive farming impacts biodiversity through:
Modern cultivars dominate while land races are lost. Wild relatives of crops — vital for breeding new disease-resistant varieties — decline with their habitats.
The UK Farmland Bird Index has fallen by more than 50% since 1970. Species such as tree sparrow (−96%), grey partridge (−93%) and turtle dove (−98%) have collapsed as hedgerows, winter stubble and insects have disappeared. Agri-environment schemes (see Lesson 6) aim to reverse these trends.
Rising global temperatures, shifting rainfall patterns and more frequent extreme weather events all threaten biodiversity. Effects include:
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