Module 4: Biodiversity

These free OCR A Level Biology Biodiversity revision notes have been written for specification points 4.2.1(a) and 4.2.1(f).

Biodiversity

Biodiversity is the measurable differences between organisms, both as individuals and as species.

Biodiversity can be considered at different levels, such as:  

• Habitat biodiversity:  The number of different ecosystems or habitat types in a defined area (e.g. woodland, grassland, sand dune and streams).
• Species biodiversity: The number of different species in a defined area (species richness) and their relative abundance (species evenness).
• Genetic biodiversity: The genetic variation between individuals of the same species.

Declining Biodiversity

Biodiversity can be reduced by both natural and human-driven (anthropogenic) factors. Human activity is currently the largest cause of biodiversity loss worldwide.

Human Population Growth

As the global population increases, demand for space, food, water, and energy also rises. This leads to:

• Habitat loss (e.g. deforestation, urbanisation)
• Pollution (e.g. air, water, and soil contamination)
• Overexploitation of natural resources (e.g. hunting, fishing, agriculture)

Agriculture

Modern farming practices often reduce biodiversity:

• Monoculture: Growing a single crop (a monoculture) across large areas eliminates habitat variety, reduces species diversity and reduces nutrients in the soil.
• Selective breeding: Reducing the genetic diversity within a domesticated species to ensure only desired characteristics are expressed (genetic erosion).
• Pesticides and herbicides: Non-target species are killed directly, or killed indirectly through contaminated food chains (e.g. bioaccumulation).

Climate Change

Changing temperature and rainfall patterns alter ecosystems, such as:

• Some species migrate to more suitable areas (if they can), and others may go extinct.
• Coral bleaching and desertification are examples of habitat loss caused by climate change.