Biodiversity in 2010
Species populations and extinction risks
The population of wild vertebrate species fell by an average of nearly one- third (31%) globally between 1970 and 2006, with the decline especially severe in the tropics (59%) and in freshwater ecosystems (41%).
Trends in the average size of species populations, as measured by the Living Planet Index (LPI), vary greatly between temperate and tropical regions, and between types of species. [Figure 2]
Temperate species populations actually increased on average since 1970, and the steady global decline since that date is accounted for entirely by a sharp fall in the tropics. This does not necessarily mean tropical biodiversity is in a worse state than in temperate regions: if the index were to extend back centuries rather than decades, populations of temperate species may have declined by an equal or greater amount. Moreover, the increase in wild animal populations in temperate regions may be linked to widespread afforestation of former cropland and pasture, and does not necessarily reflect richer diversity of species. However, the current rates of decline in global species abundance represent a severe and ongoing loss of biodiversity in tropical ecosystems.
Observed trends in populations of wild species include:
- Farmland bird populations in Europe have declined by on average 50% since 1980.
- Bird populations in North American grasslands declined by nearly 40% between 1968 and 2003, showing a slight recovery over the past five years; those in North American drylands have declined by nearly 30% since the late 1960s.
- Of the 1,200 waterbird populations with known trends, 44% are in decline.
- 42% of all amphibian species and 40% of bird species are declining in population.
Species in all groups with known trends are, on average, being driven closer to extinction, with amphibians facing the greatest risk and warm water reef-building corals showing the most rapid deterioration in status. Among selected vertebrate, invertebrate and plant groups, between 12% and 55% of species are currently threatened with extinction. Species of birds and mammals used for food and medicine are on average facing a greater extinction risk than those not used for such purposes. Preliminary assessments suggest that 23% of plant species are threatened.
Conservation interventions have reduced the extinction risk for some species, but they are outnumbered by those species that are moving closer towards extinction. The Red List Index (RLI), which tracks the average extinction risk of species over time, shows that all groups that have been fully assessed for extinction risk are becoming more threatened. [Box 4]
The most severe recent increase in extinction risk has been observed among coral species, probably due in large part to the widespread bleaching of tropical reef systems in 1998, a year of exceptionally-high sea temperatures. Amphibians are on average the group most threatened with extinction, due to a combination of habitat modification, changes in climate and the fungal disease chytridiomycosis.[Figure 3] [Figure 4] [Figure 5]
Regional trends regarding the extinction risk of species include:
- Bird species have faced an especially steep increase in extinction risk in South-East Asia, on the Pacific Islands, polar regions and in marine and coastal ecosystems.
- Mammals have also suffered the steepest increase in risk of extinction in South and South-East Asia, due to the combined impact of hunting and loss of habitat. Between ecosystem types, marine mammals have faced the steepest increase in risk, although freshwater mammals remain the most threatened.
- Amphibians have deteriorated in status fastest, and are in absolute terms at greatest risk of extinction, in South and Central America and the Caribbean.
Species of birds and mammals used for food and medicines are on average facing a greater extinction risk than species as a whole, through a combination of over-exploitation, habitat loss and other factors. Species of bird, mammal and amphibians that are exploited for food and medicines are also moving more quickly into a higher risk category. This emphasizes the threat posed by biodiversity loss to the health and well-being of millions of people directly dependent on the availability of wild species. For example the World Health Organization has estimated that 60% of children suffering from fever in Ghana, Mali, Nigeria and Zambia are treated at home with herbal medicines while in one part of Nepal, 450 plant species are commonly used locally for medicinal purposes. Globally some 80 per cent of people in developing countries rely on traditional medicines, the majority of which are derived from plants. Although global data for plants are not available, medicinal plants face a high risk of extinction in those parts of the world where people are most dependent on them for health care and income from wild collection - namely Africa, Asia, the Pacific and South America.