Biology Reference
In-Depth Information
endemic fauna of more than 500 species of cichlid fish (Seehausen et al.
1997b). Direct and indirect effects of the Nile perch have contributed to
the loss of many of these species. During the 1980s, about 200 of these
species disappeared, apparently due to predation by Nile perch. These
species lived mostly in the offshore and deep waters.The lake has experi-
enced severe eutrophication due to accelerated nutrient inputs and pre-
dation by Nile perch on herbivorous and detritus-feeding fish. Massive
growths of another alien, the water hyacinth ( Eichhornia crassipes ), have also
changed the ecology of the shallower waters.These and other factors have
contributed to further loss of species from the littoral zone. In turn,
eutrophication, increased turbidity, and reduced visibility appear to inter-
fere with color vision of many cichlids (Seehausen et al. 1997a).The result
is reduced sexual selection, incorrect mate choice, and breakdown of
reproductive isolation, leading to loss of species diversity. Other fish,
including ten species of native catfish, have also been affected, and at least
one species has become extinct (Goudswaard and Witte 1997).The Lake
Victoria ecosystem is still undergoing rapid change, and the fate of its
endemic fish fauna is still uncertain.
Alien animals have had much less impact on native plants and animals
in continental areas than in insular environments. Several forest insects,
including the gypsy moth ( Lymantria dispar ) and the adelgid scale insects
( Adelges spp.), have caused local extirpation of sensitive forest tree species
in many areas in eastern North America (Liebhold et al. 1996). Feral
domestic cats ( Felis catus ) and red foxes ( Vulpes vulpes ) have been intro-
duced or become established in many continental areas, where they prey
on native animals. In Australia, these predators have certainly contributed
to the decline of some endemic mammals, but whether or not they have
caused extinctions is uncertain (Burbridge and McKenzie 1989).
Although cats were introduced in the early 1800s and had almost com-
pletely colonized the continent by 1890, it is unlikely that they played a
substantial role in extinction of native vertebrates (Abbott 2002).
Extinction and Extirpation due to
Interspecific Competition
Invasive aliens can cause the extinction and extirpation of native species
through competition, again largely in insular environments such as
oceanic islands and fresh waters. Plants as well as animals are contributing
to these losses in some cases.
The massive transformation of native vegetation by human activity
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