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Physical
Biodiversity
Biodiversity is the variety of life on Earth, measured at the level of genes, species and whole ecosystems.
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The idea
Biodiversity is the variety of life on Earth. Scientists measure it at several levels, including the genetic variation within a species, the number of different species, and the variety of ecosystems. Life is not spread evenly. Biodiversity is greater in the tropics, thanks to the warm climate and high plant productivity near the equator. Tropical forests cover less than one-fifth of Earth's land, yet they contain about 50% of the world's species.
No one knows exactly how many species exist. A new method used in 2011 put the total number of species on Earth at about 8.7 million, with about 2.1 million of them in the ocean. Living things also do jobs that people rely on. Ecosystems supply food, wood and fresh water, and they help control the climate, pests and disease. Some of these jobs are hard to replace: insect pollination, for example, cannot be copied by people.
Biodiversity can also shrink. When a species dies out, it is gone for good. The plants and animals that depended on it may lose a food source, a partner or a home. A mass extinction is a large, sudden drop in which many groups of living things die out in a short time. Scientists study fossils from these events to learn how life recovers afterward.
Check yourself
Question 1 of 2
Why is biodiversity greater in the tropics?
Composition
what it's made of
- Genetic diversity — The variation in genes within a species.
- Species diversity — The number and variety of different species in a place.
- Ecosystem diversity — The variety of ecosystems, from forests to coral reefs.
- Phylogenetic diversity — The variety of evolutionary branches that living things belong to.
- Tropical hotspots — Tropical forests, which hold about 50% of species on less than one-fifth of the land.
Connection
how it relates
Under Ecosystems
Change
how and why it evolves
- Past
- Biodiversity grew rapidly during the Cambrian explosion, and since life began five major mass extinctions have caused sudden drops, the worst of them 251 million years ago. Vertebrate recovery from that worst extinction took 30 million years. According to Edward O. Wilson, the short word biodiversity was coined by Walter G. Rosen, who conceived the 1986 National Forum on BioDiversity.
- Now
- Human activities, especially destroying habitats for farming, are driving an ongoing loss of species and genetic diversity, and climate change adds to it. This loss is often called the Holocene extinction, or the sixth mass extinction. In 2007, scientists estimated that up to 30% of all species could be extinct by 2050.
- Next
- How much biodiversity is lost in the coming decades will likely depend on how well habitats are protected and how fast the climate changes.