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Recent extinctions described are well-documented,<ref name="Zalasiewicz"/> but the [[nomenclature]] used varies. The term [[Anthropocene]] is a term that is used by few scientists,<ref name=Zalasiewicz /> and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.<ref>{{cite book|last=Elewa|first=Ashraf M. T.|title=Mass Extinction|pages=191–194|chapter=14|isbn=978-3-540-75915-7 (Print) 978-3-540-75916-4 (Online)|url=http://www.springerlink.com/content/t576492604428l55/}}</ref> 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 (geology)|Epoch]].<ref>{{cite journal | doi = 10.1038/news031208-7 | first1= Betsy |last1= Mason | title = Man has been changing climate for 8,000 years | journal = Nature | date = 10 December 2003 }}</ref> 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. "<ref name=Zalasiewicz />
Recent extinctions described are well-documented,<ref name="Zalasiewicz"/> but the [[nomenclature]] used varies. The term [[Anthropocene]] is a term that is used by few scientists,<ref name=Zalasiewicz /> and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.<ref>{{cite book|last=Elewa|first=Ashraf M. T.|title=Mass Extinction|pages=191–194|chapter=14|isbn=978-3-540-75915-7 (Print) 978-3-540-75916-4 (Online)|url=http://www.springerlink.com/content/t576492604428l55/}}</ref> 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 (geology)|Epoch]].<ref>{{cite journal | doi = 10.1038/news031208-7 | first1= Betsy |last1= Mason | title = Man has been changing climate for 8,000 years | journal = Nature | date = 10 December 2003 }}</ref> 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. "<ref name=Zalasiewicz />
Three hypotheses have been proposed to explain the extinction of [[megafauna]] in the [[late Pleistocene]]. Of these, only two have much scientific credibility. Although Ross McPhee proposed that a hyper-disease may have been the cause of the extinction, <ref> MacPhee and Marx published their hyperdisease hypothesis in 1997. See "The 40,000-year plague: Humans, hyperdisease, and first-contact extinctions." In S. M. Goodman and B. D. Patterson (eds), Natural Change and Human Impact in Madagascar, pp 169-217, Smithsonian Institution Press: Washington DC. </ref>, the study by Lyons et al., demonstrated conclusively that a hyperdisease was unlikely to have caused the extinction. <ref> Lyons, K.S, Smith, F.A., Wagner, P.J., White, E.P, and Brown, J.H. “Was a ‘hyperdisease’ responsible for the late Pleistocene megafaunal extinction?” http://biology.unm.edu/fasmith/Web_Page_PDFs/Lyons_et_al_2004_WN.pdf </ref> The two main theories to the extinction are climate change and human hunting. The climate change theory has suggested that a change in climate near the end of the late Pleistocene stressed the megafauna to the point of extinction. <ref> Graham, R. W. and Mead, J. I. 1987. Environmental fluctuations and evolution of mammalian faunas during the last deglaciation in North America. In: Ruddiman, W. F. and H.E. Wright, J., editors. North America and Adjacent Oceans During the Last Deglaciation. Volume K-3. The Geology of North America, Geological Society of America </ref> Although this theory still has some vocal proponents, increasingly fewer scientists favor it. The best supported theory suggests early human hunting and their associated ecological impact caused the rapid extinction of the megafauna in the late Pleistocene. <ref> Martin P. S. (1967). Prehistoric overkill. In Pleistocene extinctions: The search for a cause (ed. P.S. Martin and H.E. Wright). New Haven: Yale Univ. Press. ISBN 0-300-00755-8. </ref> <ref> Lyons, S.K., Smith, F.A., and Brown, J.H. “Of mice, mastodons and men: human-mediated extinctions on four continents” http://biology.unm.edu/fasmith/Web_Page_PDFs/Lyons_et_al_2004_EER.pdf </ref>
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 [[Herbivores#Feeding strategies|browsing]] mammals, and against carnivores and scavengers which fed on both.<ref name="Martin1963">{{cite book | author = Martin P. S. | year = 1963 | title = The last 10,000 years: A fossil pollen record of the American Southwest | location = Tucson, AZ | publisher = Univ. Ariz. Press | isbn = 0-8165-1759-2}}</ref><ref name="Martin1967">{{cite book | author = Martin P. S. | year = 1967 | title = ''Prehistoric overkill. In'' Pleistocene extinctions: The search for a cause ''(ed. P.S. Martin and H.E. Wright)'' | location = New Haven | publisher = Yale Univ. Press | isbn = 0-300-00755-8}}</ref><ref name="Martin1989">{{cite book | author = Martin P. S. | year = 1989 | title = ''Prehistoric overkill: A global model. In'' Quaternary extinctions: A prehistoric revolution ''(ed. P.S. Martin and R.G. Klein)'' | pages = 354–404 | location = Tucson, AZ | publisher = Univ. Arizona Press | isbn = 0-8165-1100-4}}</ref>


==See also==
==See also==

Revision as of 23:15, 25 February 2011

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 (since around 10,000 BC). 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 2009, 875 extinctions have been documented by the International Union for Conservation of Nature and Natural Resources.[1] However, most extinctions go undocumented. According to the Species-area theory and based on upper-bound estimating, up to 140,000 species per year may be the present rate of extinction.[2]

In broad usage, Holocene extinction includes the notable disappearance of large mammals, known as megafauna, starting roughly 11,500 years ago as humans developed and spread. Such disappearances have normally been considered as either a result of global warming (the current climate change), a result of the proliferation of modern humans, or both; however in 2007 a cometary impact hypothesis was presented, but has not been broadly accepted. These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event or Ice Age extinction. However, the Holocene extinction 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, merely part of the Quaternary extinction event, or just a result of natural evolution on a non-geologic scale of time. Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction can be characterized by climate change and humanity's presence.

The prehistoric extinction events

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.

The ongoing extinction 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.

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 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.

Younger extinctions

Main articles: Oldest Dryas, Older Dryas, and Younger Dryas

New Zealand

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

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:

Ten species or subspecies of birds have disappeared from the Hawaiian islands since the 1980s. These include the Kaua'i O'o, Nukupu'u, 'Akialoa, Kama'o, Po'ouli, and others.

Madagascar

Starting with the arrival of humans around 2000 years ago, nearly all of the island's megafauna became extinct, including:

Indian Ocean Islands

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

Ongoing Holocene extinction

Wikinews has related news:

One scientist estimates the extinction may be 10,000 times the background extinction rate (the average between mass extinction events).[3][4] Most scientists predict a much lower extinction rate than this outlying estimate.[5]

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 are ecologically extinct (the Giant Panda, Sumatran Rhinoceros, North American Black-Footed Ferret, etc.) and by extinctions among arthropods. Some examples of modern extinctions of "charismatic" mammal fauna include:

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:

A 1998 poll conducted by the American Museum of Natural History found that seventy percent of biologists believe that we are in the midst of an anthropogenic extinction.[6] Numerous scientific studies—such as a 2004 report published in Nature,[7], and papers authored by the 10,000 scientists who contribute to the IUCN's annual Red List of threatened species—have since reinforced this conviction. In The Future of Life (2002), E.O. Wilson of Harvard calculated that, if the current rate of human disruption of the biosphere continues, one-half of Earth's higher lifeforms will be extinct by 2100.

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:[8] "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."[9] Some of the human causes of the current extinctions include deforestation, hunting, pollution, climate change,[10] and the introduction of non-native species

The Golden Toad of Costa Rica, extinct since around 1989. Its disappearance has been attributed to a confluence of several factors, including El Niño warming, fungus, and the introduction of invasive species.

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.[11] Extinctions that are due to human activity (anthropogenic), particularly hypothesized future events, have also been labelled the anthropocene extinction.[12][13] The Anthropocene is a term introduced in 2000.

Recent extinctions described are well-documented,[11] but the nomenclature used varies. The term Anthropocene is a term that is used by few scientists,[11] and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.[14] 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.[15] 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. "[11]

Three hypotheses have been proposed to explain the extinction of megafauna in the late Pleistocene. Of these, only two have much scientific credibility. Although Ross McPhee proposed that a hyper-disease may have been the cause of the extinction, [16], the study by Lyons et al., demonstrated conclusively that a hyperdisease was unlikely to have caused the extinction. [17] The two main theories to the extinction are climate change and human hunting. The climate change theory has suggested that a change in climate near the end of the late Pleistocene stressed the megafauna to the point of extinction. [18] Although this theory still has some vocal proponents, increasingly fewer scientists favor it. The best supported theory suggests early human hunting and their associated ecological impact caused the rapid extinction of the megafauna in the late Pleistocene. [19] [20]

See also

References

  1. ^ Summary of the 2009 update of the IUCN Red List, http://www.iucn.org/media/materials/releases/?4143/Extinction-crisis-continues-apace
  2. ^ S.L. Pimm, G.J. Russell, J.L. Gittleman and T.M. Brooks, The Future of Biodiversity, Science 269: 347–350 (1995)
  3. ^ E.O. Wilson. 2005. The Future of Life. Alfred A. Knopf. New York, New York, USA
  4. ^ C.Michael Hogan. 2010. Edenic Period. Encyclopedia of Earth. National Council for Science and Environment. ed. Galal Hassan, ed in chief Cutler Cleveland, Washington DC
  5. ^ J.H.Lawton and R.M.May, Extinction Rates, Oxford University Press, Oxford, UK
  6. ^ http://www.amnh.org/museum/press/feature/biofact.html
  7. ^ Study sees mass extinctions via warming. MSNBC. URL accessed July 26, 2006.
  8. ^ "Atlas of Population and Environment". AAAS. 2000. Retrieved 2008-02-12.
  9. ^ "Atlas of Population and Environment, Foreword". AAAS. 2000. Retrieved 2008-02-12.
  10. ^ "Measuring extinction, species by species". The Economic Times. 2008-11-06. Retrieved 2010-05-20.
  11. ^ a b c d Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1130/GSAT01802A.1, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1130/GSAT01802A.1 instead.
  12. ^ Wooldridge, S. A. (9 June 2008). "Mass extinctions past and present: a unifying hypothesis". Biogeosciences Discuss. 5. Copernicus: 2401–2423. doi:10.5194/bgd-5-2401-2008.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  13. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1073/pnas.0802812105, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1073/pnas.0802812105 instead.
  14. ^ Elewa, Ashraf M. T. "14". Mass Extinction. pp. 191–194. ISBN 978-3-540-75915-7 (Print) 978-3-540-75916-4 (Online). {{cite book}}: Check |isbn= value: invalid character (help)
  15. ^ Mason, Betsy (10 December 2003). "Man has been changing climate for 8,000 years". Nature. doi:10.1038/news031208-7.
  16. ^ MacPhee and Marx published their hyperdisease hypothesis in 1997. See "The 40,000-year plague: Humans, hyperdisease, and first-contact extinctions." In S. M. Goodman and B. D. Patterson (eds), Natural Change and Human Impact in Madagascar, pp 169-217, Smithsonian Institution Press: Washington DC.
  17. ^ Lyons, K.S, Smith, F.A., Wagner, P.J., White, E.P, and Brown, J.H. “Was a ‘hyperdisease’ responsible for the late Pleistocene megafaunal extinction?” http://biology.unm.edu/fasmith/Web_Page_PDFs/Lyons_et_al_2004_WN.pdf
  18. ^ Graham, R. W. and Mead, J. I. 1987. Environmental fluctuations and evolution of mammalian faunas during the last deglaciation in North America. In: Ruddiman, W. F. and H.E. Wright, J., editors. North America and Adjacent Oceans During the Last Deglaciation. Volume K-3. The Geology of North America, Geological Society of America
  19. ^ Martin P. S. (1967). Prehistoric overkill. In Pleistocene extinctions: The search for a cause (ed. P.S. Martin and H.E. Wright). New Haven: Yale Univ. Press. ISBN 0-300-00755-8.
  20. ^ Lyons, S.K., Smith, F.A., and Brown, J.H. “Of mice, mastodons and men: human-mediated extinctions on four continents” http://biology.unm.edu/fasmith/Web_Page_PDFs/Lyons_et_al_2004_EER.pdf

Further reading

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