What biodiversity is

The weathering mantle is the basis for the variety of vegetation, and so of biodiversity. Its deeper cause is the input of solar energy and water: places rich in both have the widest variety of life.

Biodiversity (bio = life, diversity = variety) is the number and variety of organisms in a region: the plants, animals and micro-organisms, the genes they carry and the ecosystems they form. It includes variation within and between species and within and between ecosystems. It is our living wealth.

• Today's biodiversity is the result of 2.5-3.5 billion years of evolution. Since humans appeared, it has been declining fast, with species after species lost through overuse.
• Estimates of the number of species range from 2 million to 100 million; 10 million is the best estimate. New species are found all the time; about 40 per cent of South America's freshwater fish are thought to be still unclassified.
• A species lasts on average 1-4 million years; 99 per cent of all species that ever lived are now extinct.
• Biodiversity is richest in the tropics; towards the poles there are larger populations of fewer species.

Three levels of biodiversity:

• Genetic diversity: variation of genes within a species. (A species is a group of organisms with similar physical characteristics.) All humans are Homo sapiens, yet we differ in height, colour and appearance: that is genetic diversity. It is essential for healthy breeding.
• Species diversity: the variety and number of species in a defined area, measured by richness, abundance and types. Areas very rich in species are hotspots of diversity.
• Ecosystem diversity: the broad differences between ecosystem types and the variety of habitats and ecological processes within each. Ecosystem boundaries are not rigid, so they are hard to draw.

Example (new): India's many traditional rice varieties (some drought-tolerant, some flood-tolerant, some scented) are genetic diversity within one species; the Western Ghats' mix of shola forest and grassland side by side is ecosystem diversity.