|
Since 1800, many species of plants, insects
and other living things have become
extinct and many more are threatened
with extinction. Thus far, scientists have
been able to gather data on the number of
extinct or threatened species of three classes
of animals - birds, reptiles, and mammals. According to the United Nation's
International Union for the Conservation of
Nature and Natural Resources (IUCN), more
than 40 kinds of freshwater fish have become
extinct in the past century in North America.
Rivers that once teemed with prized sportfish,
such as salmon, have been depleted as
people built dams, widened channels, and
constructed irrigation networks. Some fish
species have been killed off because people
released foreign fish species and other
animals into the waterways that competed
with the native species for food.
Australia, which has long been known
as a land of fascinating mammals -
particularly the kangaroos and koalas - has
also faced some problems. Of the 40 species
of the world's mammals that are known to
have become extinct during the last two
centuries, 18 were native to Australia.
Scientists blame the impact of agriculture
on natural habitats and the release of
foxes and other foreign species.
The southern tip of Africa is home to a
unique ecological community called the
fynbos, which supports an extraordinary
variety of plants - about 8500 species.
Many of these species are shrub-like plants
that bear tiny flowers of many colors. In
the past century, 36 species have become
extinct and more than 600 others are at risk
of extinction, primarily because people have
brought in foreign plants that compete with
the fynbos for space and sunlight.
In the Mississippi and St Lawrence river
basins of North America, naturalists once
identified nearly 300 native species of
freshwater clams and mussels. Of these, 21
have become extinct since the late 1800s,
and another 120 are at risk of extinction.
Scientists say the construction of dams and
canals and the pollution of waterways by
fertiliser and sewage brought about this
rapid decline in shellfish populations.
At first glance, amphibians appear to
be a bright spot in the global picture. Only
five out of more than 4000 species of frogs,
toads and other varieties are known to have
vanished in the past century. However,
ecologists have recorded massive declines in
the populations of amphibians worldwide
since the 1970s. Many declines occurred
in areas that appear to be undisturbed by
human activity.
The global nature of these declines is
particularly troubling because it suggests
that there is widespread pollution of the
atmosphere. Populations may be declining
because pollution damages amphibian eggs
before the young can hatch. Many ecologists
predict that unless human activities change
dramatically, we are likely to lose one-half of
the world's species during the next 100 years.
Such estimates may appear extreme, but
scientists point out that archaeological records
show that rapid extinction of species followed
the spread of human beings across the globe.
And we already know of thousands of plant;
and animal species of which only specimens
in museums remain. Today's massive and
rapidly growing human population is
capable of much greater damage. |
