AQA GCSE Biology: Biodiversity

Biodiversity is the variety of life, and keeping it high is important for the health of ecosystems and for our own future. This guide explains what biodiversity is, why it matters, and the steps being taken to protect it. The idea to hold onto is that variety makes ecosystems more stable.

What biodiversity is

Biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.

Variety, not number. A wood holding ten thousand oaks and nothing else has an enormous number of organisms and almost no biodiversity. A wood holding a few hundred each of forty species has far fewer organisms and far more. Questions that give you two sets of survey data are usually testing exactly that distinction.

Why biodiversity matters

Good levels of biodiversity are important for several reasons.

• They ensure the stability of ecosystems, by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment (for example, tree roots keep the soil stable).
• They help ensure the future of the human species, for example because we rely on pollinators for our food crops.

The first of those two is the one students explain badly, so it is worth unpicking. Variety makes an ecosystem stable because it removes single points of failure. If a caterpillar is the only food a bird eats, a bad year for caterpillars is a bad year for the bird. If the bird eats six things, losing one of them barely registers. The same logic runs through pollination, shelter and the physical structure of the place, which is why tree roots holding soil together is given as an example: lose the trees and the soil itself washes away, and everything living in it goes too.

The second reason is more direct. Roughly three quarters of the crop types we eat depend on animal pollinators, so a fall in insect numbers is not only an ecological problem but a food supply one. This is the argument that gets made in six mark questions about why biodiversity matters to humans, and it is stronger than any general appeal to nature being valuable.

Many human activities are reducing biodiversity, and only recently have steps been taken to try to stop this.

Maintaining biodiversity

A number of programmes aim to reduce the negative effects of humans on ecosystems.

• Breeding programmes for endangered species, to prevent extinction.
• Protecting and regenerating rare habitats, such as coral reefs.
• Reintroducing field margins and hedgerows on farms that grow a single crop.
• Reducing deforestation and carbon dioxide emissions, to slow global warming.
• Recycling resources rather than dumping waste in landfill.

Those five are not equally powerful, and a good answer says so. A breeding programme saves one species at a time and depends on there still being somewhere to put it back. Protecting the habitat saves everything living in it at once, including the species nobody has got round to counting. Where a question asks which measure would do most, habitat protection is usually the stronger answer, with breeding programmes as the last resort for a species already close to extinction.

Field margins and hedgerows are the example worth being able to explain, because the mechanism is small and specific. A field planted edge to edge with one crop is a monoculture, which supports very few species. Leaving a strip of uncropped land round the edge gives insects, small mammals and birds somewhere to feed and nest, and the hedgerows link those strips together so populations are not isolated from one another.

Every one of these measures also has a cost, and questions often ask for the other side. Field margins take land out of production, protecting a habitat can block development or farming that people depend on, and recycling schemes need money and public cooperation. Being able to name a real conflict is usually worth a mark on its own.

How this fits together

One of the main threats to biodiversity is pollution from human waste, which is the subject of the pollution and waste guide.