Biodiversity yields many direct human benefits:
- genetic material for crop and livestock breeding;
- chemicals for new medicines;
- aesthetic beauty, wonder, and adventure that generates ecotourism revenues.
More important, the diversity of species undergirds the ability of an ecosystem to provide most of its other goods and services. Reducing the biological diversity of an ecosystem may well diminish its resilience to disturbance, increase its susceptibility to disease outbreaks, and decrease its productivity.
The erosion of global biodiversity over the past century is alarming. Major losses have occurred in virtually all types of ecosystems, much of it by simple loss of habitat area.
- Forest cover has been reduced by more than 20 percent worldwide, with some forest ecosystems, such as the dry tropical forests of Central America, virtually gone.
- More than 50 percent of the original mangrove area in many countries is gone; wetlands area has shrunk by about half; and grasslands have been reduced by more than 90 percent in some areas.
- Only tundra, arctic, and deep-sea ecosystems have emerged relatively unscathed, although human pressures are apparent even in these.
Even if ecosystems had retained their original spatial extent, many species would still be threatened by pollution, overexploitation, competition from invasive species, and habitat degradation.
- In terms of the health of species diversity, freshwater ecosystems are far and away the most degraded, with some 20 percent of freshwater fish species extinct, threatened, or endangered in recent decades.
- Forest, grassland, and coastal ecosystems all face major problems as well.
- The rapid rise in the incidence of diseases affecting marine organisms, the increased prevalence of algal blooms, and the significant declines in amphibian populations all attest to the severity of the threat to global biodiversity.
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| Agroecosystems | Coastal ecosystems | Forest ecosystems | Freshwater systems | Grassland ecosystems |
