Biodiversity

Biodiversity means the variety of life on Earth: how many different species there are, how different they are from each other, and how varied the ecosystems they form are. The word combines biological and diversity. Earth's biodiversity is the result of 3.7 billion years of evolution and is one of the most precious things we have. Right now, biodiversity is in serious trouble: scientists estimate species are going extinct 100 to 1,000 times faster than the natural background rate. Protecting biodiversity is one of the most important challenges of our time.

• Species knownapprox. 2 millionOfficially described and named
• Estimated total8 to 10 millionMost still undiscovered
• Insectsapprox. 80%Of all animal species are insects
• Biodiversity hotspotRainforestsapprox. 50% of all species, on 6% of land
• Current extinction rate100 to 1,000xFaster than the natural background
• Species at riskapprox. 1 millionOf total extinction in coming decades

Three levels of biodiversity

Biologists usually break biodiversity into three different levels.

• Genetic diversity: the variety of genes within a single species. Different breeds of dog or varieties of apple have different genetic diversity. High genetic diversity helps a species adapt to changes.
• Species diversity: the number of different species in an area. A rainforest has very high species diversity; a wheat field has very low species diversity.
• Ecosystem diversity: the variety of different ecosystems in a region. A country with forests, mountains, deserts, wetlands and coral reefs has high ecosystem diversity.

All three levels matter. A species with low genetic diversity is fragile (one disease could wipe it out). An area with low species diversity is unstable (losing one species could collapse the whole food web). And a planet with only one or two kinds of ecosystem is poor and vulnerable.

Where biodiversity is highest

Biodiversity is not spread evenly across the world. Some areas are unbelievably rich, others almost empty. The richest areas are usually:

• Tropical rainforests (Amazon, Congo, South-East Asia): less than 6% of Earth's land but home to roughly 50% of all known species.
• Coral reefs: cover less than 1% of the ocean floor but contain about 25% of all marine species.
• Mediterranean climates: the Cape region of South Africa, southern California and central Chile have extraordinarily rich plant diversity in small areas.
• Island archipelagos: islands often have unique species found nowhere else (the lemurs of Madagascar, the marsupials of Australia, the finches of the Galapagos).

Why biodiversity matters

Biodiversity is not just nice to have: it is essential for the way the planet works and for the way human societies survive.

• Ecosystem services: pollination, water purification, soil building, climate regulation, all depend on a wide variety of species working together.
• Food security: humans currently get most of our calories from just a few species (wheat, rice, maize). Genetic diversity in these and other crops is our defence against future pests, diseases and climate change.
• Medicine: about 25% of modern drugs were first discovered in plants or animals. Aspirin came from willow bark. The chemotherapy drug Taxol came from a yew tree.
• Climate stability: forests, peatlands, wetlands and oceans store enormous amounts of carbon. Losing them speeds up climate change.
• Cultural and spiritual value: nature inspires art, religion, science and identity in every culture on Earth.
• Resilience: complex ecosystems with many species are more able to absorb shocks (droughts, fires, disease outbreaks) than simple ones.

Why biodiversity is in trouble

Biodiversity is being lost at a frightening rate. Scientists estimate that current extinction rates are 100 to 1,000 times the natural background rate. Around 1 million species are currently at risk of total extinction within the coming decades. The main reasons are all human:

• Habitat loss: forests cleared for farms, wetlands drained, grasslands ploughed, coral reefs destroyed.
• Climate change: rising temperatures, shifting rainfall, ocean warming and acidification are pushing species beyond their tolerance.
• Pollution: pesticides, plastics, fertiliser runoff and industrial chemicals damage ecosystems.
• Over-exploitation: too much hunting, fishing and harvesting.
• Invasive species: humans accidentally or intentionally introducing species to new places where they out-compete the natives.

Fact About 40% of the world's insect species are now in decline, and over a third may be at risk of extinction within decades. This matters not just for insects but for everything that depends on them: birds, fish, frogs, lizards, bats and the 75% of food crops that need insect pollinators. The loss of insects is sometimes called the "insect apocalypse" and is one of the most worrying ecological trends of our time.

What is being done

The picture is not hopeless. Conservation works when it is properly funded and well managed. Some recent success stories:

• Bald eagles: down to 417 nesting pairs in the US in the 1960s; now over 300,000, thanks to a ban on the pesticide DDT.
• Giant pandas: numbers up by over 50% since the 1980s thanks to Chinese habitat protection.
• Humpback whales: hunted to near-extinction by the mid-20th century, now recovering well thanks to whaling bans.
• California condor: down to 22 birds in 1987; over 500 today thanks to captive-breeding programmes.
• European bison: extinct in the wild in 1927, brought back from zoo populations and now numbering over 6,000 in the wild.

Major international agreements like the Convention on Biological Diversity and the 30 by 30 goal (to protect 30% of Earth's land and seas by 2030) aim to slow the loss. Individual countries also pass laws to protect specific species and habitats.

Did you know? The most biodiverse country in the world is Brazil, mostly because it contains over half of the Amazon rainforest. Brazil has more known species of plants, freshwater fish, mammals, amphibians and probably insects than any other country on Earth. The Amazon basin alone may contain over 10% of all the species on the planet.

Deeper dive: why we should care about species we will never see

One question often comes up when discussing biodiversity: why should we care about a tiny obscure species we will never see, in a forest we will never visit? Biologists give a number of answers, and not all of them are about practical use to humans.

Hidden value. Many species turn out to have unexpected practical importance. The fungus Penicillium was discovered to make penicillin almost by accident in 1928 and went on to save tens of millions of lives. The Australian platypus inspires modern military sensors that detect electrical fields. The chemicals in poison dart frogs are being studied as new painkillers. Almost every "useless" species could turn out to have value we have not yet discovered. Once it is extinct, that chance is gone forever.

Connections we do not understand. Ecosystems are immensely complex. Losing a small species can cascade in ways we cannot easily predict. The small obscure beetle might be the favourite food of the songbird that pollinates the forest flowers. Losing the beetle might lose the bird; losing the bird might lose the flowers; losing the flowers might lose the trees. Removing single species from food webs has caused dramatic collapses again and again.

Ethical value. Many people argue that other species have a right to exist regardless of their usefulness to us. We share the planet with millions of other living things, and we did not create any of them. Some religious traditions see protecting nature as a moral duty. Many indigenous cultures see other species as relatives rather than resources.

Beauty and wonder. Life on Earth is the most extraordinary thing in the known universe. Every species is the unique result of billions of years of evolution. Losing a species is losing a story that took 4 billion years to write. Many people simply think the world is a richer, more meaningful place with all its variety intact.

For the loss of life over time, see extinction. For how ecosystems work, see what is an ecosystem.