Habitat fragmentation and destruction

Despite the potential importance of altered nutrient-cycles and pollution, the primary immediate threat to biodiversity is from habitat loss that results from expanding human populations and their economic activities. Habitat loss includes outright destruction as well as habitat disturbance due to fragmentation and localized pollution. In many areas of the world including Europe, China, south and Southeast Asia, Madagascar, Oceania, and much of the United States, most original habitat has already been destroyed. Today the highest annual deforestation rates are in developing and tropical countries, where a large proportion of the world's biodiversity is found. The countries having the highest rates of deforestation in the early twenty-first century are Costa Rica (3.0% annual loss of remaining forest cover), Thailand (2.6%), Vietnam (1.4%), Ghana (1.3%), Laos P.D.R. (1.2%), and Colombia (1.2%). Threats to savannas, grasslands, and freshwater aquatic systems are less well documented, but they are as important as deforestation—and, like deforestation, are concentrated within economically poor countries that are rich in biodiversity. This is a matter considered later in the present essay.

One typical result of environmental alteration is the isolation of habitat fragments, or patches. Fragmentation can reduce or prohibit the dispersal of individuals, and local extinction of some species becomes more likely. Later this essay considers some consequences of habitat fragmentation.

A small koala clings to the back of a German shepherd dog in a koala park near Brisbane, Australia. (Photo by © Kit Kittle/Corbis. Reproduced by permission.)
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