What biodiversity means
Biodiversity, short for biological diversity, is the variety of life. Scientists usually describe it at three connected levels.
- Genetic diversity is the variety of genes within a species. A population with lots of genetic variation contains individuals with different traits, such as different resistance to a disease.
- Species diversity is the number and mix of species in an area. A tropical forest typically holds many more species than a field of a single crop.
- Ecosystem diversity is the variety of habitats and communities, such as wetlands, forests, grasslands and reefs, across a landscape or the world.
It is not just a head count of species. A place with ten equally common species is generally seen as more diverse than one with ten species where one makes up almost every individual. Where biodiversity is highest is also uneven: it is usually greater toward the tropics and in places with varied terrain and climates, though there are many exceptions.
Variety as insurance
One of the central ideas about biodiversity is that variety acts like insurance. Different species respond differently to heat, drought, floods, pests and disease. If a community has many species doing similar jobs, then when one declines, others may take over its role. This is sometimes called functional redundancy.
Experiments in grasslands, for example, have found that plots with more plant species tend to be more productive and to recover better from drought than plots with few species. Results of such studies differ with site and conditions, and ecologists continue to debate how general the pattern is, but the broad conclusion that variety tends to stabilize ecosystem function is widely accepted.
The same logic applies within species. A crop or animal population with little genetic variety can be wiped out by a single disease that all individuals are vulnerable to. A historical example commonly cited is the Irish potato famine in the 1840s, when the potatoes grown were genetically very similar and were devastated by a blight. The causes of that famine were also social and political, so biodiversity is only part of the story. More generally, variation is also the raw material that natural selection acts on, allowing populations to adapt over time.
What biodiversity does for people
Many of the benefits that ecosystems provide to humans depend on living variety. Often these are called ecosystem services.
- Food. People eat a few hundred species out of many thousands of edible ones, but crops depend on pollination, soil organisms and pest-controlling insects, and plant breeders use the genes of wild relatives to improve resistance and yield. The work of plant pollination is a good example.
- Clean water and soil. Wetlands, forests and soil organisms filter water, hold soil in place and cycle nutrients.
- Medicine and materials. Many medicines were first found in or modeled on natural compounds, such as the antibiotic penicillin from a mold. It is hard to know what undiscovered species might offer, but claims about miracle cures hidden in rainforests are often exaggerated.
- Climate and hazards. Forests, peatlands and oceans store carbon, and coastal mangroves and reefs can reduce the force of waves.
- Culture and well-being. Wildlife and natural places hold recreational, spiritual and aesthetic value for many people.
Because many of these services come free, their value is easy to overlook until they are lost and have to be replaced by costly human alternatives.
Does every species matter equally?
Not every species has the same effect. Keystone species, such as some top predators or ecosystem engineers like beavers, have a larger influence than their numbers would suggest. Other species may be easily replaced by neighbors with similar roles. Ecologists are still working to understand which losses matter most in a given ecosystem and how many can be lost before functions fail. It is hard to predict in advance, which is one reason many conservationists favor caution.
There is also a view that species have value in their own right, apart from their use to humans. That is an ethical position rather than a scientific finding, and people hold a range of views on it.
What threatens biodiversity
The main pressures are the same ones described in the article on species extinction: habitat loss and fragmentation, overharvesting, invasive species, pollution and climate change. Many assessments conclude that global biodiversity is declining, though the pace and pattern differ between regions and groups of organisms. Some places have seen species increase locally, and some species have recovered thanks to protection. Local species counts can also stay the same while the mix changes, as common generalists replace rare specialists, so a simple count may hide what is being lost.
What supports it
Approaches to conserving biodiversity include protecting large and connected areas of habitat, restoring degraded land and waters, managing fisheries and forests sustainably, controlling invasive species and keeping crop and livestock varieties. Farming methods that keep hedgerows, ponds and varied crops can support wildlife alongside food production. Conservation has trade-offs, and the costs and benefits often fall on different people, so local communities are important partners.
A healthy ecosystem is one that can keep working through shocks, and variety is a big part of what makes this possible. Biodiversity cannot guarantee that an ecosystem will never change, but it generally gives living systems more options.