Wikipedia:Holocene extinction

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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 mammals that ate their eggs.

The Holocene extinction is the widespread, ongoing extinction of species during the present 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. 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 go undocumented, scientists estimate that during the 20th century, between 20,000 and two million species actually 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 may be regarded as continuing into the 21st century.

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 (however the period was characterized by a sudden change in global temperature known as the Little Ice Age for which there is no accepted explanation) and its rather short geological timescale (tens to thousands of years) compared to recent small extinctions.

The prehistoric extinction events

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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.

Younger extinctions

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.

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.
• The Nēnē-nui, or Woodwalking Goose, an extinct species of goose that once inhabited Maui.
• A giant megapode from New Caledonia.
• Mekosuchine crocodiles from New Caledonia, Fiji and Samoa.

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

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.

Ongoing Holocene extinction

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Significantly, the rate of species extinctions at present is estimated at 100 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 populations of animals that are 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 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.

Human influence on extinction

Extinction of animals and plants caused by human actions may go as far back as the late Pleistocene.^[8] Extinctions that are due to human activity (anthropogenic), particularly hypothesized future events, have also been labelled the anthropocene extinction event^[9] or anthropocene mass extinction.^[10] The Anthropocene is a term introduced in 2000.

Recent extinction events described are well-documented,^[8] , but the nomenclature used varies. The term Anthropocene is not formally defined,^[8] and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction event,^[11] which incorporates both the earlier Quaternary extinction event and the later Anthropocene extinction event.^{[citation needed]} The Holocene-Anthropocene boundary is contested, with some commentators asserting significant human influence on climate for much of what is normally regarded as the Holocene Epoch.^[12] Other commentators place the Holocene-Anthropocene boundary at the industrial revolution while also saying that "Formal adoption of this term in the near future will largely depend on its utility, particularly to earth scientists working on late Holocene successions. "^[8]

The extinction of megaherbivores in the late Pleistocene is explained by one of two hypotheses, or a combination of the two: climate change, and the ecological impact of early humans. Not only hunting, but anthropogenic fire selected for the survival of ruminants more than the survival of browsing, and against carnivores and scavengers which fed on both.^[13][14][15]

See also

• Slash and burn
• Timeline of extinctions
• Deforestation
• Extinction risk from climate change
• List of extinct plants
• List of extinct animals
• Global warming

References

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" (^{[dead link]} – ^{Scholar search}). 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. 

External links

• "NATIONAL SURVEY REVEALS BIODIVERSITY CRISIS - SCIENTIFIC EXPERTS BELIEVE WE ARE IN MIDST OF FASTEST MASS EXTINCTION IN EARTH'S HISTORY". http://www.amnh.org/museum/press/feature/biofact.html. Retrieved 2008-08-03. 
• "An Interview with Dr. Peter Raven, director of the Missouri Botanical Garden". http://news.mongabay.com/2007/0312-interview_peter_raven.html. Retrieved 2008-08-03. 
• Firestone RB, West A, Kennett JP, et al. (October 2007). "Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling". Proc. Natl. Acad. Sci. U.S.A. 104 (41): 16016–21. doi:10.1073/pnas.0706977104. PMID 17901202.