Human Impact on Biodiversity (AQA A-Level Biology): Revision Notes

Human Impact on Biodiversity

Impact of agriculture on species diversity

Human activities, particularly agriculture, have significantly reduced biodiversity worldwide. The need to produce sufficient food at low cost has led to substantial changes in natural environments.

Natural ecosystems develop gradually over time, creating complex communities containing numerous individuals from many different species. These mature systems typically display high levels of diversity. In contrast, agricultural ecosystems are managed and controlled by humans, resulting in fundamentally different ecological characteristics.

Farmers select crop varieties and livestock breeds for specific productive qualities, which reduces the genetic diversity of alleles present in farmed species. To maintain economic viability, large numbers of these selected species must be grown or reared in concentrated areas. Since any given area can only support a limited amount of biomass, when most space and resources are occupied by farmed species, little room remains for other organisms.

This creates intense competition for the limited space and resources available. Many wild species cannot compete effectively and fail to survive. Even species that adapt to these changed conditions often experience severely reduced population sizes. Additionally, pesticides are frequently applied to eliminate organisms that compete with crops for light, mineral nutrients, water, and food. The combined result is a marked decrease in species diversity, with agricultural ecosystems showing consistently low diversity indices.

The balance between conservation and farming

Growing human populations create mounting pressure for more intensive food production. In the UK, food output has doubled over the past 40 years through several approaches: improved genetic varieties of crops and livestock, increased use of chemical fertilisers and pesticides, expanded biotechnology applications, and changes in farming methods leading to larger farms and conversion of natural land to agricultural use.

While these changes have successfully increased food production, they have also diminished the variety of habitats within ecosystems and consequently reduced species diversity.

Direct habitat removal

Several farming practices directly remove habitats and reduce species diversity:

• Removal of hedgerows and clearing of woodland areas
• Creation of monocultures by replacing diverse natural meadows with single crop species or grass for silage
• Filling in ponds and draining marshland and wetland areas
• Over-grazing of land, particularly upland areas by sheep, which prevents woodland regeneration

Indirect effects on biodiversity

Other agricultural practices create more subtle but equally significant impacts:

• Application of pesticides and inorganic fertilisers that affect non-target species
• Pollution from effluent escaping from silage stores and slurry tanks into water systems
• Lack of crop rotation and absence of intercropping or undersowing practices

Conservation techniques in agriculture

Despite the apparent conflict between intensive food production and conservation, numerous management approaches can increase species and habitat diversity without significantly raising costs or reducing yields.

Boundary and habitat management

Maintaining existing hedgerows at optimal height and shape provides better wildlife habitats than rectangular boundaries. A-shaped hedge profiles offer superior habitat conditions compared to rectangular cutting. Planting hedges rather than installing fences creates more effective field boundaries while supporting biodiversity.

Preserving existing ponds and creating new water features where feasible supports aquatic and semi-aquatic species. Leaving wet corners of fields undrained rather than draining them maintains important microhabitats.

Tree and vegetation strategies

Planting native tree species in areas with low species diversity proves more beneficial than planting in already species-rich locations. Creating natural meadows and using hay rather than intensive grass crops for silage supports diverse plant communities.

Leaving vegetation at field edges uncut until after flowering and seed dispersal allows plants to complete their reproductive cycles and provides food resources for wildlife.

Chemical and crop management

Reducing pesticide use through biological control methods or developing genetically modified crops resistant to specific pests decreases environmental impact. Using organic rather than inorganic fertilisers supports soil ecosystem health.

Implementing crop rotation that includes nitrogen-fixing crops improves soil fertility naturally while reducing dependence on artificial fertilisers. Using intercropping rather than herbicides to control weeds and pests provides a more sustainable approach to crop protection.

Conservation headlands

Establishing conservation headlands - areas at field edges where pesticides are used restrictively - allows wild flowers and insects to flourish while maintaining crop production in the main field areas.

Financial incentives from organisations such as the Department for Environment, Food and Rural Affairs (DEFRA) and the European Union help encourage farmers to adopt these practices, recognising that biodiversity maintenance is essential for global ecosystem stability.

Species extinction and habitat loss in the UK

Current species extinction rates are estimated to be 100-1000 times higher than natural background rates throughout evolutionary history. The primary cause of species loss is habitat clearance and conversion to grow crops and accommodate increasing human populations. An area of rainforest approximately the size of the UK is cleared globally each year.

UK habitat loss data

Significant habitat loss has occurred in the UK since 1900, with conservation agencies documenting the percentage of various habitat types that have disappeared:

• Grassland habitats have experienced the most severe losses - hay meadows have declined by 95% and chalk grasslands by 80%, primarily due to conversion to highly productive grass and silage operations.
• Wetland areas show substantial losses with lowland fens and wetlands reduced by 50% through drainage and land reclamation for agriculture.
• Woodland and heath habitats have declined significantly - lowland mixed woodland and lowland heaths on acid soils have both decreased by 40%, mainly through conversion to commercial forestry and farmland.
• Field boundaries such as hedgerows have decreased by 30% as farmers create larger fields to accommodate modern farm machinery.
• Other habitat losses include limestone pavements in England (45% removed for sale as rockery stone) and various other specialised ecosystems.