T H E “ S I X T H W A V E ”
The rapid loss of species that we are witnessing today is estimated by some experts to be between 100 and 1,000 times higher than the “background” or expected natural extinction rate (this is a highly conservative estimate: some studies estimate current extinction rates as 1,000–11,000 times background rates). Unlike the mass-extinction events of geological history, the current extinction phenomenon is one for which a single species - ours - appears to be almost wholly responsible. Such a deteriorating situation is being referred to as “the sixth extinction crisis”, after the five known extinction waves in the Ordovican, Devonian, Permian, Triassic and Cretaceous Periods.
The frequently asked question of “how many species have gone extinct in the last 100 years” is difficult to answer because of problems in recording contemporary extinction events. Decline and eventual extinction may take place over many years, or even centuries in the case of very long-lived organisms like some of the large mammal and tree species.
The final stages of extinction are seldom observed except those caused by extreme events such as the excessive hunting of the passenger pigeon (Ectopistes migratorius) or the mass extinction of native snails in French Polynesia and Hawaii following the introduction of the predatory snail (Euglandina rosea) to Pacific Islands. Since 1500 AD, 844 extinctions have been recorded.
P R O F I L E S I N R E D
The 2004 IUCN Red List of Threatened Species tells us that the global extinction crisis is as bad, or worse, than we believed.
A total of 15,589 species of plants and animals are known to face a high risk of extinction in the near future, in almost all cases as a result of human activities. This includes 32% (one in three) of amphibian species, 24% (one in four) of mammal species, 12% (one in eight) of bird species, 25% (one in four) of conifers and 52% of cycads (an ancient group of plants).
Indonesia, India, Brazil and China are among the countries with the most threatened mammals and birds, while plant species are declining rapidly in South and Central America, Central and West Africa, and Southeast Asia.
The IUCN Red List highlights the plight of a range of animals and plants, from the Pemba flying fox to the King Pilly pine.
Aders duiker (Cephalophus adersi). This antelope which occurs in Kenya and Tanzania moved from Endangered to Critically Endangered since 2003 because of substantial population declines caused by declining habitat and illegal hunting.
The state of the world’s threatened bird species is worse than ever. Since 1994 the number of bird species threatened with global extinction has risen to 12%. Of the new total, 1,175 (99%) are at risk of extinction from human activities.
Sao Tome free-tailed bat(Chaerephon tomensis). This bat has moved up the threatened scale from Vulnerable to Critically Endangered. It is known to occur in only two sites, despite extensive searches. Its coastal forest and savanna habitats are being destroyed through tourism and agricultural development.
The number of threatened reptiles increased from 253 in 1996 to 304 in 2004. The number of Critically Endangered species has increased from 41 to 64 and Endangered from 59 to 79 species.
St Helena olive (Nesiota elliptica). Listed in 2003 as Extinct in the Wild, this symbolic species is now Extinct. The last known tree surviving in the wild died in 1994 and the only known plant still in cultivation died in November 2003. No other live material (plants, seeds or tissues) remain in local or international collections.
A total of 8,321 threatened plants are listed. This is around 2% of the world’s described plants, but as only approximately 4% of the world's described plants have been evaluated, the true percentage of threatened plant species is much higher.
Giant Hispaniolan galliwasp (Celestus warreni). Moving from Near Threatened to Critically Endangered, this lizard is thought to have declined by at least 80% over the last 20 years. It is threatened by habitat loss, especially deforestation for agricultural activities (planting crops and creating pastures). The galliwasp is also killed by local people who mistakenly consider it to be venomous. Galliwasps are also killed by dogs, cats and mongooses.
Almost all the factors that have led to the extinction of species in the modern era continue to operate, many with ever-increasing intensity. While these factors vary in intensity and relative importance in the three major biomes (the land, inland waters and the seas), certain common threads emerge.
Major threats to ecosystems and biological diversity (biodiversity) are:
• Over exploitation (extraction, hunting, fishing etc.)
• Pollution
• Invasions of alien species (e.g. cats and rats on Ascension Island)
• Global climate change (changes in migratory species patterns, coral bleaching, etc.)
Habitat Loss and Degradation is the most pervasive threat to birds, mammals and amphibians, affecting 86% of all threatened birds, 86% of the threatened mammals assessed and 88% of the threatened amphibians.
Exploitation, including hunting, collecting, fisheries and fisheries by-catch, and the impacts of trade in species and species' parts, constitutes a major threat for birds (30% of threatened birds), mammals (33% of threatened mammals),amphibians (6% of threatened amphibians), reptiles and marine fishes.
Alien Invasive Species are a significant threat, affecting 326 (30%) of all threatened birds, and 212 threatened amphibian species (11%). The commonestcause of extinction of bird species since 1800, especially those on islands, is theintroduction of alien invasive species such as the black rat.
source : http://www.countdown2010.net/documents/Extinction_media_brief_2004.pdf
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