Biodiversity and its importance, sampling and monitoring ecosystems using quadrats, transects and indicator species, the human activities that reduce biodiversity, and the methods used to maintain biodiversity such as conservation, reforestation and protecting habitats.

What this dot point is asking

OCR wants you to define biodiversity and explain why it matters, describe how ecosystems are sampled and monitored (including using indicator species), explain the human activities that reduce biodiversity, and describe the methods used to maintain it.

Biodiversity and why it matters

Biodiversity matters for several reasons OCR expects you to give:

• Stability. Species in a community are interdependent, so a varied ecosystem with many species and food chains is more stable and copes better if one species declines. Low biodiversity makes an ecosystem fragile.
• Resources for humans. Wild species provide food, materials and the source of many medicines, and the gene pool for future crops.
• Ecosystem services. Living things provide pollination of crops, recycling of nutrients, clean water and a stable atmosphere.

The future of the human species on Earth relies on maintaining a good level of biodiversity, which is why so many human activities that reduce it are a concern.

Monitoring ecosystems

Scientists monitor ecosystems to detect change over time. Two approaches are examined:

• Sampling with quadrats (to estimate population size or percentage cover) and transects (to study how distribution changes across a habitat). Repeating a survey over years shows whether a population is rising or falling. This is the fieldwork you met in topic B4.
• Indicator species. Some species are very sensitive to particular conditions, so their presence or absence indicates the level of pollution. Lichens indicate clean air (they die where sulfur dioxide pollution is high). Certain freshwater invertebrates (such as mayfly larvae and freshwater shrimp) indicate clean, well-oxygenated water, while others (such as sludgeworms and rat-tailed maggots) tolerate polluted water.

Human activities that reduce biodiversity

A number of human activities reduce biodiversity, often by destroying or polluting habitats:

• Deforestation for timber, farmland or building destroys habitats and reduces the number of species.
• Pollution of air, water and land harms or kills organisms (for example sewage reducing oxygen in rivers).
• Using land for farming, housing, industry and quarrying, and for landfill, removes habitats.
• Peat bog destruction, draining wetlands for farming, releases stored carbon dioxide and destroys habitats.

Maintaining biodiversity

Conservation aims to slow or reverse the loss of biodiversity. Methods include:

• Reforestation and replanting hedgerows to restore habitats.
• Protecting habitats by creating nature reserves and national parks and by legal protection of endangered species.
• Breeding programmes in zoos and seed banks to protect species at risk of extinction.
• Reducing deforestation and pollution, and recycling to reduce the land used for landfill.

Many of these involve a balance between conservation and human needs such as food and development, so OCR may ask you to weigh the costs and benefits.