may directly affect prey species, or they may compete with other species for limited re-
sources. If such resources as water and food are limited during habitat destruction, then
species can become extinct.
Another type of habitat that is being rapidly destroyed is the wetland. By the 1980s, over
80% of all historic wetlands in seven states of the U.S. were filled, at which time Congress
acted to create a policy of “no net loss” of wetlands. In Europe, extensive loss of wetlands
has resulted in loss of biodiversity. For example, many bogs in Scotland have been drained
or developed because of human population expansion. Over half of the Portlethen Moss in
Aberdeenshire, for example, has been lost and a number of species, such as the great crested
newt, are no longer present.
Another example of species loss due to habitat destruction occurred on Madagascar’s central
highland plateau. From 1970 to 2000, slash and burn agriculture eliminated about 10% of
the country’s total native biomass and converted it to a barren wasteland. Adverse effects
included widespread gully erosion that produced heavily silted rivers and eliminated a large
amount of usable fresh water. Much of the riverine ecosystems of several large west-flowing
rivers were also destroyed, several fish species have been driven to the edge of extinction,
and some coral reef formations in the Indian Ocean are effectively lost.
Practices such as clear-cutting of old growth forests, strip mining (Figure25.30), and drift-
net fishing can go beyond the harvesting of a single species or resource to degrade entire
ecosystems. Overexploitation happens on the level of genes and ecosystems as well as indi-
vidual species. Forest plantations, fish hatcheries and farms, and intensive agriculture reduce
both species diversity and genetic diversity within species.
Figure 25.30: Strip coal mining, pictured here, has degraded the entire ecosystem. ( 6 )