The variety of living things around us is one of the greatest wonders of life on earth. Unfortunately this variety is being steadily reduced by the actions of people. This has serious consequences for the future.

Remarkably, we do not know the true number of species on earth. More than 1,4 million have been identified, and it is estimated that the absolute number is between 5 and 30 million! Human destruction of the natural world is so serious that millions of these species are doomed to become extinct before they have even been named.

The biodiversity found on earth is the result of 3,6 billion years of evolution. A natural part of the evolutionary process is extinction, where species disappear owing to changes in their living conditions which they are unable to survive. In recent times, however, the rate of extinction has increased dramatically and is estimated to be 1000 to 10 000 times greater than before human intervention.

LOSS OF BIODIVERSITY - THE CAUSES

* Habitat loss:
All plants and animals rely on their habitat (the area where they live), for food, water, shelter and living space. Growing human populations requiring land for agricultural, industrial and urban development are destroying species' habitat on a huge scale.

* Pollution:
Various forms of pollution contribute to the loss of plants and animals. For example, marine turtles often mistake plastic bags floating in the sea for jelly fish, and eat them. This may choke turtles to death or prevent them from eating properly. Scavenging birds are vulnerable to poison baits put out by farmers in an attempt to control stock predators.

* Wildlife trade:
The huge international trade in wildlife threatens many species with extinction. Despite laws passed to protect threatened species, potential profits make illegal dealing worth the risk. For example, the rhino is hunted for its horn which is prized in Eastern countries as a dagger handle and for supposed medicinal properties.
Cycads and many succulent plants are also traded illegally, whilst many parrot species are collected for the wild bird trade.

* Alien species:
When an alien species is introduced to an area it may have advantages which allow it to survive better than indigenous species, and thus may threaten these local species with extinction. Cape fynbos, for example, is threatened by Australian acacias which were originally brought in to stabilise the dunes. Alien species sometimes interbreed with indigenous species, as has happened with the domestic cat and the African wild cat.

* Poaching and hunting:
This is often, but not always, linked to trade in a particular species. The African wild dog, for example, has been in conflict with stock farmers for a long time and has been hunted relentlessly, making it Africa's most threatened carnivore.

THE IMPORTANCE OF BIODIVERSITY

Possibly the most important reason for the maintenance of biodiversity is summed up by American conservationist, Aldo Leopold: "The first rule of intelligent tinkering is to save all the parts."

The variety of life on earth forms a huge gene pool which is the material on which natural selection works in the ongoing process of evolution, which generates more biodiversity. This gene pool is also a resource of crucial importance to humanity for food, fuel, clothing, shelter, and to maintain our health. Biodiversity enhances our lives in countless ways, from the development of new and improved food crops and medicines, to the sight of a flight of geese against a sunset. While modern technology has given people greatly increased power over nature, it has done little to reduce our dependence on biodiversity.

Living things do not exist independently of each other, or the non-living environment. They depend on one another in a variety of ways: think, for example, of a food chain. Together with the non-living parts of our environment (e.g. soil, water, air), living things form essential life-support systems such as the water cycle, the carbon cycle and several other nutrient cycles. The pool of life is therefore much more than the sum of its parts.

WHAT YOU CAN DO

* Demands for goods and services place pressure on the environment - the less we use, the less severe the pressure.

* When a conservation issue rears its head, make your voice heard - draw up a petition, contact your local MP, write to the Department of Environment Affairs and liaise with your newspaper.

* Become informed and talk about this issue to your friends, family and colleagues.

* Support a conservation organisation.

Many people believe that every species has the right to exist, and that our role as custodians of the planet is to ensure their survival.

DID YOU KNOW

* Tropical rain forests are the world's most important areas of species diversity, containing over half the world's species on just 7% of the earth's land surface. They are being destroyed so rapidly that most will disappear within the next century.

FURTHER READING

SOUTH AFRICA'S THREATENED WILDLIFE. J. Ledger. Endangered Wildlife Trust, Johannesburg, 1990.

THE GAIA ATLAS OF PLANET MANAGEMENT. N. Myers (ed). Pan Books, London, 1985.

GOING GREEN: PEOPLE, POLITICS AND ENVIRONMENT IN SOUTH AFRICA. J. Cock and E. Koch (eds). Oxford University Press, Oxford, 1991.

SOUTH AFRICAN ENVIRONMENTS INTO THE 21ST CENTURY. B. Huntley, R. Siegfried and C. Sunter. Human, Rousseau and Tafelberg, Cape Town, 1989.

BIODIVERSITY. E. Wilson (ed). National Academy Press, Washington D.C., 1988.

BIOLOGICAL DIVERSITY. A pamphlet available from WWF-SA. Address below.

Enviro-Facts: "Why Conserve?" and "Biodiversity in South Africa".

USEFUL ADDRESSES

Department of Environment Affairs and Tourism. P/Bag X 447, Pretoria, 0001. Tel. 012-310 3425.

WWF-SA. P.O. Box 456, Stellenbosch, 7600. Tel. 021-887 2801.