Holocene extinction event

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The Dodo, a bird of Mauritius, became extinct during the mid-late seventeenth century after humans destroyed the forests where the birds made their homes and introduced animals that ate their eggs.

The Holocene extinction event is the widespread, ongoing mass extinction of species during the modern Holocene epoch. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; a sizeable fraction of these extinctions are occurring in the rainforests. This extinction event is sometimes referred to as the sixth extinction following the previous five extinction events. Between 1500 and 2006 CE, 784 extinctions have been documented by the International Union for Conservation of Nature and Natural Resources.^[1] However, since most extinctions are likely to go undocumented, scientists estimate that during the 20th century, between 20,000 and two million species became extinct, but the precise total cannot be determined more accurately within the limits of present knowledge. Up to 140,000 species per year (based on Species-area theory)^[2] may be the present rate of extinction based upon upper bound estimating.

In broad usage, the Holocene extinction event includes the notable disappearance of large mammals, known as megafauna, starting 10,000 years ago as humans developed and spread. Such disappearances have been considered as either a response to climate change, a result of the proliferation of modern humans, or both. These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event or Ice Age extinction event. However the Holocene extinction event continues into the 21st century.

The observed rate of extinction has accelerated dramatically since the 1950s. There is no general agreement on whether to consider more recent extinctions as a distinct event or merely part of a single escalating process. Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction event is most significantly characterised by the presence of human-made driving factors and its very short geological timescale (tens to thousands of years) compared to most other extinction events.

[edit] The prehistoric extinction events

The ongoing extinction event seems more outstanding in light of separating recent extinctions (approximately since the industrial revolution) from the Pleistocene extinction near the end of the last glacial period. The latter is exemplified by the extinction of the woolly mammoth and, incorrectly, the Neanderthal people.

However, modern climatology suggests the current Holocene epoch is no more than the latest in a series of interglacial intervals. Furthermore, there is a continuum of extinctions since 11,000 years BCE. If only considering human impact, the vulnerability and extinction rate of species simply rises with the increase in human population, so there would be no need to separate the Pleistocene extinction from the recent one. Nevertheless, the Pleistocene extinction event is large enough and has not been resolved completely.

[edit] Younger extinctions

Please refer to main articles: Oldest Dryas, Older Dryas, and Younger Dryas

[edit] New Zealand

c. CE 1500, several species became extinct after Polynesian settlers arrived, including:

Ten species of Moa, giant flightless ratite birds.
The giant Haast's Eagle, Harpagornis
The flightless predatory Adzebills.

[edit] Pacific, including Hawaii

Recent research, based on archaeological and paleontological digs on 70 different islands, has shown that numerous species went extinct as people moved across the Pacific, starting 30,000 years ago in the Bismarck Archipelago and Solomon Islands (Steadman & Martin 2003). It is currently estimated that among the bird species of the Pacific some 2000 species have gone extinct since the arrival of humans (Steadman 1995). Among the extinctions were:

The Moa-nalos, giant grazing ducks from Hawaii.
A giant megapode from New Caledonia.
Mekosuchine crocodiles from New Caledonia, Fiji and Samoa.

[edit] Madagascar

Starting with the arrival of humans in the first century BCE or first century CE, nearly all of the island's megafauna became extinct, including:

Eight or more species of elephant birds, giant flightless ratites in the genera Aepyornis and Mullerornis.
17 of 50 species of lemur, including:
- Giant aye-aye (Daubentonia robusta)
- sloth lemurs, including chimpanzee-sized Palaeopropithecus and gorilla-sized Archaeoindris
- Megaladapis, an orangutan-sized arboreal lemur
Giant Fossa
Two species of Malagasy Hippopotamus

[edit] Indian Ocean Islands

Starting c. 1500 CE, a number of species became extinct upon human settlement of the islands, including:

several species of giant tortoise on the Seychelles and Mascarene Islands
14 species of birds on the Mascarene Islands, including the Dodo, the Rodrigues Solitaire, and the unrelated Réunion Solitaire.

[edit] Ongoing Holocene extinction

Wikinews has related news: Largest mass extinction in 65 million years underway, scientists say

Significantly, the rate of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the evolutionary time scale of planet Earth.^[3]

Megafaunal extinctions continue into the 21st century. Modern extinctions are more directly attributable to human influences. Extinction rates are minimized in the popular imagination by the survival of captive trophy populations of animals that are "merely" extinct in the wild (Père David's Deer, etc.), by marginal survivals of highly-publicized megafauna that is ecologically extinct (Giant Panda, Sumatran Rhinoceros, the North American Black-Footed Ferret, etc.) and by unregarded extinctions among arthropods. Some notable examples of modern extinctions of "charismatic" mammal fauna include:

Aurochs, Europe
Tarpan, Europe
Thylacine or Tasmanian Tiger, Thylacinus cynocephalus, Tasmania [extinction disputed]
Quagga, a zebra relative, Southeast Africa
Steller's Sea Cow
Falkland Island Fox

Many birds have become extinct as a result of human activity, especially birds endemic to islands, including many flightless birds (see a more complete list under extinct birds). Notable extinct birds include:

the Dodo, the giant flightless pigeon of Mauritius, Indian Ocean
the Great Auk of islands in the north Atlantic
the Passenger Pigeon of North America
several species of Moa, giant flightless birds from New Zealand
the Carolina Parakeet of the American southeast

Most biologists believe that we are at this moment at the beginning of a tremendously accelerated anthropogenic mass extinction. E.O. Wilson of Harvard, in The Future of Life (2002), estimates that at current rates of human disruption of the biosphere, one-half of all species of life will be extinct by 2100. In 1998 the American Museum of Natural History conducted a poll of biologists that revealed that the vast majority of biologists believe that we are in the midst of an anthropogenic mass extinction. Numerous scientific studies since then—such as a 2004 report from Nature,^[4] and those by the 10,000 scientists who contribute to the IUCN's annual Red List of threatened species—have only strengthened this consensus.

Peter Raven, past President of the American Association for the Advancement of Science, states in the foreword to their publication AAAS Atlas of Population and Environment:^[5] "We have driven the rate of biological extinction, the permanent loss of species, up several hundred times beyond its historical levels, and are threatened with the loss of a majority of all species by the end of the 21st century."^[6] The reasons for the current mass extinction are all human related and include deforestation and other habitat destruction, hunting and poaching, the introduction of non-native species, pollution and climate change with the United Nations estimating that the world is facing its worst extinction period since the dinosaurs became extinct 65 million years ago.^[7]

The Golden Toad of Costa Rica, extinct since around 1989. Its disappearance has been attributed to climate change.

Evidence for all previous extinction events is geological in nature, and the shortest scales of geological time are in the order of several hundred thousand to several million years. Even those extinction events that were caused by instantaneous events — the Chicxulub asteroid impact being currently the demonstrable example — unfold through the equivalent of many human lifetimes, due to the complex ecological interactions that are unleashed by the event.

There was a limited debate as to the extent to which the disappearance of megafauna at the end of the last glacial period can also be attributed to human activities, directly, by hunting, or indirectly, by decimation of prey populations. While climate change is still cited as another important factor, anthropogenic explanations have become predominant.

189 countries which are signatory to the Rio Accord have committed to preparing a Biodiversity Action Plan, a first step at identifying specific endangered species and habitats, country by country.

[edit] See also

[edit] References

^ 2006 version of IUCN redlist, http://www.iucn.org/bookstore/HTML-books/Red%20List%202004/completed/Executive%20Summary.html
^ S.L. Pimm, G.J. Russell, J.L. Gittleman and T.M. Brooks, The Future of Biodiversity, Science 269: 347-350 (1995)
^ J.H.Lawton and R.M.May, Extinction rates, Oxford University Press, Oxford, UK
^ Study sees mass extinctions via warming. MSNBC. URL accessed July 26, 2006.
^ "Atlas of Population and Environment". AAAS. 2000. http://atlas.aaas.org/. Retrieved on 2008-02-12.
^ "Atlas of Population and Environment, Foreword". AAAS. 2000. http://atlas.aaas.org/index.php?sub=foreword. Retrieved on 2008-02-12.
^ Measuring extinction, species by species

[edit] Further reading

Leakey, Richard; Lewin, Roger (1996). The Sixth Extinction: Patterns of Life and the Future of Humankind. New York: Anchor Books. ISBN 0385468091.
Martin, P. S.; Wright, H. E. Jr. (eds.) (1967). Pleistocene Extinctions: The Search for a Cause. New Haven: Yale University Press. ISBN 0300007558.
Ted Oakes (2003). Land of Lost Monsters: Man Against Beast--The Prehistoric Battle for the Planet. Hylas Publishing. ISBN 1-59258-005-X.
Steadman, D. W. (1995). "Prehistoric extinctions of Pacific island birds: biodiversity meets zooarchaeology". Science 267 (5201): 1123–1131. doi:10.1126/science.267.5201.1123.
Steadman, D. W.; Martin, P. S. (2003). "The late Quaternary extinction and future resurrection of birds on Pacific islands". Earth Science Reviews 61 (1–2): 133–147. doi:10.1016/S0012-8252(02)00116-2. http://www.eeb.cornell.edu/donlan/readings/Steadman%20and%20Martin%202003.pdf.