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Freshwater biodiversity: Although freshwater ecosystems such as rivers, lakes and wetlands occupy less than 2% of the Earth's total land surface, they provide a wide range of habitats for a significant proportion of the world's plant and animal species. |
Although many are yet to be discovered, the number of freshwater species worldwide is estimated at between 9 000 and 25 000 (Cosgrove and Rijsberman, 2000). This number is rapidly decreasing due to human interference. |
| Freshwater Species Population Index |
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Between 1970 and 1999, the Freshwater Species Population Index fell by nearly 50%, which constitutes a very rapid decline in population indices.
The Freshwater Species Population Index measures the average change over time in the populations of some 194 species of freshwater birds, mammals, reptiles, amphibians and fish. The index represents the average of six regional indices, which measure freshwater species populations in Africa, Asia-Pacific, Australasia, Europe, Latin America and the Caribbean, and North America. There has been a much smaller decline over the past 30 years in the freshwater species of North America and Europe than those in the other regions. Much of the loss and degradation of freshwater ecosystems in the industrialised world took place prior to 1970. The status of freshwater bird and mammal populations is better known than those of other groups. Waterfowl are among the most closely monitored of all wild species. Much less is known about population trends among freshwater fish and amphibians, although many biologists believe these to be among the most threatened classes of species in the world. Recent evidence suggests there has been a drastic decline in amphibian populations in many parts of the world since the 1950s. Source: Loh, 2000. |
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Physical alteration, habitat degradation, excessive water withdrawal and pollution have contributed directly or indirectly to the decline in freshwater species. |
Other factors that reduce freshwater biodiversity include the incursion of non-native species and the mismanagement of inland fisheries. Today, an estimated 20% of the world's freshwater fish are vulnerable, endangered or extinct (Revenga et al., 1998). |
