A4.2 Conservation of biodiversity

Biodiversity is the variety of life, and it is being lost faster now than at almost any time in Earth’s history — so fast that many biologists describe the present as a sixth mass extinction, this time driven by a single species: us. A4.2 connects the science of measuring and valuing biodiversity with the practical question of how to protect it. The key understanding for the exam is that biodiversity exists at several levels, that human activity is the main current threat, and that conservation works best when it combines protecting habitats with safeguarding individual species.

What biodiversity means

Biodiversity is more than just a count of species. The syllabus recognises three levels:

• Species diversity — the number of different species in an area and the relative abundance of each. A community with many species, each reasonably common, is more diverse than one dominated by a single species.
• Genetic diversity — the variety of alleles within a species. High genetic diversity gives a population a better chance of adapting to change and resisting disease.
• Ecosystem diversity — the range of different habitats and ecosystems in a region, from coral reefs to rainforests to wetlands.

These levels are linked: losing ecosystems removes species, and shrinking populations lose genetic diversity, leaving them less able to adapt.

The biodiversity crisis and its causes

Extinction is a natural process, but the current rate of extinction is far higher than the natural background rate, and it is overwhelmingly caused by human activity. The major anthropogenic causes include:

• Habitat destruction and fragmentation — the single biggest cause, as land is cleared for agriculture, settlement and resource extraction.
• Overexploitation — hunting, fishing and harvesting faster than populations can recover.
• Pollution of air, water and soil.
• Invasive (alien) species that outcompete or prey on native organisms.
• Climate change, which shifts the conditions species are adapted to faster than many can track.

Evidence for the crisis comes from monitoring populations and assessing extinction risk — the IUCN Red List classifies species into categories such as vulnerable, endangered and critically endangered. Trends recorded over time show many populations declining, supporting the conclusion that an extinction crisis is underway.

Why conserving biodiversity matters

The case for conservation rests on several kinds of value:

• Economic and practical value: wild species provide food, medicines, materials and the genetic resources used to improve crops.
• Ecological value: species provide ecosystem services such as pollination, nutrient cycling, water purification and climate regulation. Removing species can destabilise whole ecosystems.
• Ethical and aesthetic value: many people argue species have an intrinsic right to exist, and natural environments have cultural and recreational importance.

Because the loss is, in practical terms, irreversible — an extinct species cannot be recovered — conservation is often framed as protecting options for future generations as well as present ones.

In situ and ex situ conservation

Conservation methods fall into two broad approaches. In situ conservation protects species in their natural habitat, for example through nature reserves and protected areas. This is generally the preferred approach because it conserves whole communities and the interactions between species, and it allows populations to keep evolving in response to their environment. Its success depends on reserves being large enough and properly managed.

Ex situ conservation protects species outside their natural habitat, using zoos, botanic gardens, captive-breeding programmes and seed banks. It is valuable as a backup when habitats are too degraded, for breeding endangered species to boost numbers, and for storing genetic material. Its drawbacks are that it can support only limited numbers, organisms may lose adaptations to the wild, and reintroduction is difficult. The most effective conservation strategies often combine the two — for instance breeding animals ex situ and then reintroducing them into protected habitat.