In biology and ecology, extinction
is the cessation of existence of a species or group of taxa, reducing
biodiversity. The moment of extinction is generally considered to be the death
of the last individual of that species.
More than 90 percent of all
organisms that have ever lived on Earth are extinct. As new species evolve to
fit ever changing ecological niches, older species fade away. But the rate of
extinction is far from constant. At least a handful of times in the last 500
million years, 50 to more than 90 percent of all species on Earth have
disappeared in a geological blink of the eye.
about 65 million years ago, probably caused or aggravated by impact of
several-mile-wide asteroid that created the Chicxulub crater now hidden on the
Yucatan Peninsula and beneath the Gulf of Mexico. Some argue for other causes,
including gradual climate change or flood-like volcanic eruptions of basalt lava
from Indias Deccan Traps. The extinction killed 16 percent of marine families,
47 percent of marine genera (the classification above species) and 18 percent of
land vertebrate families, including the dinosaurs.
End Triassic extinction,
roughly 199 million to 214 million years ago, most likely caused by massive
floods of lava erupting from the central Atlantic magmatic province -- an event
that triggered the opening of the Atlantic Ocean. The volcanism may have led to
deadly global warming. Rocks from the eruptions now are found in the eastern
United States, eastern Brazil, North Africa and Spain. The death toll: 22
percent of marine families, 52 percent of marine genera. Vertebrate deaths are
about 251 million years ago. Many scientists suspect a comet or asteroid impact,
although direct evidence has not been found. Others believe the cause was flood
volcanism from the Siberian Traps and related loss of oxygen in the seas. Still
others believe the impact triggered the volcanism and also may have done so
during the Cretaceous-Tertiary extinction. The Permian-Triassic catastrophe was
Earths worst mass extinction, killing 95 percent of all species, 53 percent of
marine families, 84 percent of marine genera and an estimated 70 percent of land
species such as plants, insects and vertebrate animals.
Late Devonian extinction,
about 364 million years ago, cause unknown. It killed 22 percent of marine
families and 57 percent of marine genera. Erwin said little is known about land
organisms at the time.
about 439 million years ago, caused by a drop in sea levels as glaciers formed,
then by rising sea levels as glaciers melted. The toll: 25 percent of marine
families and 60 percent of marine genera.
There are now 41,415
species on the IUCN Red List and 16,306 of them are threatened with extinction,
up from 16,118 last year. The total number of extinct species has reached 785
and a further 65 are only found in captivity or in cultivation.
Estimates of global species
diversity have varied from 2 million to 100 million species, with a best
estimate of somewhere near 10 million, and only 1.75 million known species of
living organisms on earth have been identified.
biological impoverishment of the Earth is accelerating as human
population grows. The share of bird, mammal, and fish species that are
now in danger of extinction is in double digits - 11 percent of all bird
species, 25 percent of mammals, and 34 percent of fish. Over
19,000 plant species and 5000 animal species are classified as endangered.
threatened species are at risk from human activities.
are home to 50 to 70% of all life forms on Earth. Coral
and the Oceans are home to 25% to 30% of all life forms. At the current rate
of destruction how long will it be before human beings become endangered?
estimate an average of 137
species of life forms are driven into extinction every day
for a total of 50,000
Many species are being
put at risk of extinction on a daily basis
The threats to wildlife are:
Many animals are hunted and killed for their body parts to be used for ornamental
decoration as well as in superstitious potions. Currently, the demand for
animal parts is centered in several parts of Asia where there is a strong
market for traditional medicines made from items like tiger bone and rhino horn.
Many animals are also killed for food ,this is referred to as bushmeat.
More and more land is being claimed by Man for his own ends.
Centuries may be required to bring back a forest that was cut down or burnt out
in the space of a few years. Many of the world's severely threatened animals and
plants live in such forests, and it is certain that huge numbers of them will
disappear if present rates of forest loss continue.
and toxins that Man is releasing into the air and water causes an imbalance in
ecosystems. Contamination of air, water, or soil by the discharge of harmful
substances contribute to species extinction.
The change in temperature and climate is affecting species that dwell on land as
well as the ocean.
Concern is growing that atmospheric changes could bring
on rapid, profound climatic changes. A slight rise in maximum water
temperatures - only one to two degrees can cause coral bleaching.
rise in temperature can bleach coral like this
Exotic Species-Species that "belong" to an area are said to be
native species. Exotic Species are interlopers, foreign elements introduced
intentionally or accidentally into new settings through human activities.
Exotics may seriously disrupt delicate ecological balances and create a cascade
of unintended consequences.
to the World Wildlife Federation (WWF) the most endangered species are:
Spiny dogfish - Spiny
dogfish is a slender, smaller sized white-spotted shark that grows to about
one metre long and travels in schools. It is found in cool, coastal waters
worldwide. Known as rock salmon, it is used in fish and chips in the UK and
as a smoked meat delicacy in Germany, called Schillerlocken.
Sawfish - Populations
of the seven species of sawfish have drastically declined. They are traded
as live animals for public aquariums, and also for their fins and meat.
Their distinctive saw-like snouts are sold as souvenirs and ceremonial
weapons, while other body parts are used for traditional medicines.
Tigers - In addition
to continuing threats from habitat loss and forest conversion, an old threat
is about to re-emerge in China, which could put the last remaining tigers
further at risk - the potential re-opening of trade from tiger 'farms'.
Asian rhinos -
Historically hunted for their horn, a prized ingredient in traditional Asian
medicines, and devastated by the destruction of their lowland forest
habitat, Asian rhino populations are now distressingly small. An upsurge in
poaching over the last few is taking its toll even on populations that were
thought to be stable.
Red and pink coral -
A jewel that comes from reefs and atolls, it is the most valuable of all the
precious corals. Pink coral has been fished for over 5,000 years and used
for jewellery and decoration. Over-harvesting and the destruction of entire
colonies by bottom trawls and dredges have led to dramatic population
European eel - The
European eel comes from coastal and freshwater ecosystems throughout Europe,
including Mediterranean countries. Stocks have declined dramatically over
the past several decades due to overfishing and poaching. There is
significant international demand for this species, both for live juvenile
eels (shipped from Europe to Asia) for rearing in aquaculture and for the
highly valued meat of adults.
Elephants - The
ongoing poaching of elephants and illegal international trade in ivory is
stimulated by rampant ivory sales in some countries, particularly in Africa
and Asia. Despite previous CITES decisions, and valiant efforts of some
countries, these markets persist. The time has come to put political will
behind serious efforts to close down these illegal and unregulated ivory
markets, the true driver of elephant poaching.
Great apes - Wild
populations of great apes (gorillas, bonobos, chimpanzees and orangutans),
continue to decline drastically and are threatened by the combined effects
of illegal trade in live animals (usually for pets), poaching for meat,
disease and habitat disturbance, fragmentation and destruction.
just don't understand how humans can be so careless
Cetaceans-Seven out of
the 13 great whale species are still endangered or vulnerable after decades
of protection. Facing a multitude of hazards Whales, dolphins and porpoises
are succumbing to new and ever-increasing dangers. Collisions with ships and
entanglement in fishing gear threaten the North Atlantic right whale with
extinction, while the Critically Endangered Western North Pacific gray whale
is at serious risk because of intensive oil and gas development in its
feeding grounds. Alarm is also growing over other hazards including toxic
contamination, the effects of climate change and habitat degradation. It's
illegal, but it still happens: commercial whaling Despite a moratorium on
commercial whaling and the declaration of virtually the whole of the
Southern Ocean as a whale sanctuary, each year over 1,000 whales are killed
for the commercial market.
Bigleaf mahogany -
This highly valuable South and Central American rainforest tree species was
listed in CITES Appendix II in 2002, in response to population declines and
high levels of illegal logging and trade. Only one country still exports
large commercial quantities, Peru, and after five years, these problems
continue, and concerted action is needed.
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To Find Out More
about Endangered Species Visit The Organizations Below