Loss of biodiversity

It is doubtful whether speciation is adding new species today, but species are certainly being lost, and human activities are clearly to blame.

When humans colonised the tropical Pacific Islands, over 2,000 native bird species are said to have gone extinct.

The IUCN Red List (2004) records the extinction of 784 species in the last 500 years: 338 vertebrates, 359 invertebrates and 87 plants.

Recent extinctions: the dodo of Mauritius, the quagga of Africa, the thylacine of Australia, Steller's sea cow of Russia, and three tiger subspecies (Bali, Javan, Caspian). In the last twenty years alone, 27 species have disappeared.

Extinctions are not random across taxa; some groups, such as amphibians, appear more vulnerable.

More than 15,500 species worldwide face the threat of extinction: 12 per cent of bird species, 23 per cent of mammal species, 32 per cent of amphibian species and 31 per cent of gymnosperm species.

Over more than 3 billion years of life there have been five mass extinctions. The 'Sixth Extinction' now under way differs in rate: 100 to 1,000 times faster than in pre-human times, because of human activities. If trends continue, nearly half of all species could be lost within the next 100 years.

Losing biodiversity in a region can cause (a) a fall in plant production, (b) weaker resistance to environmental perturbations such as drought, and (c) greater variability in ecosystem processes: plant productivity, water use, and the cycles of pests and diseases.