What is biodiversity?
Biodiversity is the variety of life on Earth. It is usually described at three levels:genetic diversity (differences between individuals of the same species), species diversity (how many different species there are and how evenly they are spread), and ecosystem diversity (the range of habitats, from coral reefs to grasslands). Scientists have described about 2 million species, but there may be 8 million or more.
Diversity and stability
Ecosystems are constantly disturbed by droughts, storms, pests and diseases. In a diverse community, species react differently: when a drought kills a shallow-rooted grass, a deep-rooted plant or a drought-tolerant clover may survive and expand into the space. Total plant growth stays more stable even though individual species rise and fall. This is known as the insurance hypothesis: the more species there are, the more likely it is that some will cope with whatever happens.
The experiment behind the model
At Cedar Creek in Minnesota, ecologist David Tilman and colleagues planted 168 grassland plots with between 1 and 16 species and measured them for decades. Plots with more species produced more plant growth and varied much less from year to year. During severe droughts, diverse plots lost far less productivity and recovered faster. Similar results have since been found in many experiments around the world.
Why biodiversity matters to people
- Food security: crop diversity and wild relatives protect against pests and diseases. The Irish potato famine of the 1840s struck a country depending on very few potato varieties.
- Pollination: about three quarters of food crops benefit from animal pollinators.
- Clean water and air, fertile soils and flood control all depend on healthy ecosystems.
- Medicines: many drugs, from aspirin to cancer treatments, come from wild organisms.
Keystone species
Some species matter far more than their numbers suggest. Sea otters eat sea urchins; without otters, urchins strip kelp forests bare. Beavers build dams that create wetlands used by hundreds of other species. Losing akeystone species can cause an entire ecosystem to change.
Threats to biodiversity
The main causes of biodiversity loss today are habitat loss from farming and building,overexploitation through overfishing and hunting, climate change,pollution and invasive species. Wildlife populations monitored worldwide have fallen by around two thirds on average since 1970, and about a million species are estimated to be at risk of extinction.
Protecting biodiversity
Protected areas, habitat restoration, wildlife corridors that link habitats, sustainable farming and fishing, controlling invasive species, and seed banks all help. Even small actions, such as leaving wildflower patches for pollinators, add up.
Interesting facts
- Scientists have named roughly 2 million species, but estimates of the total number on Earth run to several million more, most of them insects and other small organisms.
- Tropical rainforests cover only a small fraction of Earth’s land yet are thought to hold around half of all land species.
- The Philippines is one of the world’s biodiversity hotspots, with many species found nowhere else, such as the Philippine eagle and the tarsier.
Key terms
- Monoculture
- Growing a single species over a large area.
- Resistance / resilience
- How little an ecosystem changes during a disturbance / how quickly it recovers afterwards.
- Ecosystem services
- The benefits people get from nature, such as food, clean water and pollination.
Common misconceptions
- “Biodiversity just means lots of animals.” It includes plants, fungi, microbes, genes and habitats.
- “Losing one species doesn’t matter.” Each loss removes a role and a backup in the ecosystem; keystone losses can be dramatic.
- “Monocultures are always more productive.” Diverse systems often match or exceed them, and are far more stable.
Key takeaways
- Biodiversity is the variety of genes, species and ecosystems.
- Diverse ecosystems resist disturbances better and recover faster.
- Different species use resources in different ways, often making diverse systems more productive.
- Habitat loss is the leading cause of biodiversity decline.
Model note: species traits are invented for the demonstration and the plots are simplified. The pattern, more stability with more species, matches long-term field experiments.