Global overview

Biodiversity resources

Biodiversity refers to the variability among living organisms from all sources, including terrestrial, marine and other aquatic ecosystems, and the ecological complexes of which they are part. This includes diversity within species (genetic diversity), between species and of ecosystems.

There is no universally accepted classification of ecosystems at the global scale (UNEP 1995) but Olson (1994) defined 94 ecosystem classes based on land cover, vegetation and climate. This framework provides a mechanism for summarizing data at the global level, while recognizing the distinctiveness of ecosystems within each individual region.

Estimated number of described species
Kingdom	Described species
Described species	4 000
Protoctists (algae, protozoa, etc.)	80 000
Animals: vertebrates	52 000
Animals: invertebrates	1 272 000
Fungi	72 000
Plants	270 000
Total described species	1 750 000
Possible total including unknown species	14 000 000
Source: UNEP-WCMC 2000

Tropical forest ecosystems are the most speciesrich environments. Although they cover less than 10 per cent of the world's surface, they may contain 90 per cent of the world's species. Coral reefs and Mediterranean heathland are also highly species-rich. Around 1.75 million species have been named by taxonomists to date (UNEP-WCMC 2000). The total number of species has recently been estimated as 14million (see table), although this is highly uncertain, due to a lack of information about the number of insect, nematode, bacteria and fungus species.

Living organisms contribute to a wide variety of environmental services, such as regulation of the gaseous composition of the atmosphere, protection of coastal zones, regulation of the hydrological cycle and climate, generation and conservation of fertile soils, dispersal and breakdown of wastes, pollination ofmany crops, and absorption of pollutants (UNEP 1995). Many of these services are neither widely recognized nor properly valued in economic terms; however, the combined economic value of 17 ecosystem services has recently been estimated in the range US$16-54 trillion per year (Costanza and others 1997).

Human health and well-being are directly dependent on biodiversity. For example, 10 of the world's 25 top-selling drugs in 1997 were derived from natural sources. The global market value of pharmaceuticals derived from genetic resources is estimated at US$75 000-150 000 million annually. Some 75 per cent of the world's population rely for health care on traditional medicines, which are derived directly from natural sources (UNDP, UNEP, World Bank and WRI 2000).

Biodiversity also provides genetic resources for food and agriculture, and therefore constitutes the biological basis for world food security and support for human livelihoods. A number of wild crop relatives are of great importance to national and global economies. For example, Ethiopian varieties have provided protection from viral pathogens to California's barley crop, worth US$160 million per year. Genetic resistance to disease obtained from wild wheat varieties in Turkey has been valued at US$50 million per year (UNEP 1995).