Only about one third of earth’s forests are untouched by humans. Even when disturbed areas are reforested, many do not support the same species as those which originally inhabited the area (Stokstad, 2008). Between 1960 and 1990, 20% of all the earth’s
rainforests were cut. During this
Islands frequently carry species that occur
nowhere else in the world. For
example, of the 135 birds that occurred only in
About 140,000 square kilometers of tropical rainforest are cut/year. During the 1990s, the earth’s forest cover decreased by 4% and about half of the world’s forests have been lost since the dawn of agriculture. More than half the earth’s wild wetlands have been lost during the past century.
Due to population growth alone, the percentage of species in an average nation is expected to rise to about 7% by the year 2020 and 14% by 2050. Human population growth is a primary factor in an estimated 88% of the species whose condition is considered threatened (McKee, 2003).
Habitat fragmentation can stress amphibian populations by increasing the distance between adult habitats and breeding areas (Becker, 2007). Many animals
which inhabit deep woods habitats are threatened when a habitat is fragmented,
not only because the physical area that they can inhabit is reduced, but
also because new species are introduced into the area which compete with
them. This is especially evident in the case of brown-headed cowbirds.
Many animals which inhabit deep woods habitats are threatened when a habitat is fragmented, not only because the physical area that they can inhabit is reduced, but also because new species are introduced into the area which compete with them. This is especially evident in the case of brown-headed cowbirds.
The brown headed cowbird parasitizes
other birds by laying its eggs in their nests. Other birds raise the cowbirds
as their own and the cowbird nestlings outcompete those of the other species.
This brood parasitism can decrease the populations of songbirds by half.
The brown headed cowbird originally inhabited western North America but
expanded its populations eastward when forests were cleared. They prefer
edge habitats so that the splitting of a large region of continuous forest
into smaller habitats drastically increases the effect of cowbirds on
Extinction is a natural process; it is estimated that over 99.9% of all the living things that have ever existed in earth's history are now extinct. Sometimes extinction occurs at a slow rate; there are other times known as mass extinctions.
Due to the human impact on the natural world, it is estimated that at least 100 species become extinct every day; at this rate, the mass extinction through which we are now living will soon (by the year 2000?) surpass the Cretaceous extinction and become the 2nd largest in earth's history.
Why aren’t you aware of the species which become extinct every day?
1) They are Rare:
at the list of endangered species in
2) Most people are unfamiliar with many groups of organisms, such as insects, freshwater mollusks, etc. Ninety-five percent of all animal species are invertebrates and therefore many species could go extinct from your area without your being aware of them ever existing.
Since most of
the species on earth do not even occur in the
There are a number of organisms on the Endangered
Species List that have not been seen in years/decades and may already
be extinct such as the turgid blossom, yellow blossom, little Mariana
fruit bat, Mariana mallard, scioto madtom. The Bachman’s warbler and Ivory billed woodpecker
are extinct from the
Some species that inhabited