The Holocene extinction refers to the 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. 875 extinctions occurring between 1500 and 2009 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 disappearance of large mammals, known as megafauna, starting roughly 11,500 years ago due to abrupt climate change at the end of the last Ice Age. Such disappearances have normally been considered as either a result of climate change, or 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. 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.
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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 large herbivores such as the woolly mammoth and the carnivores that preyed on them.
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.
c. 1500, several species became extinct after Polynesian settlers arrived, including:
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.
Starting with the arrival of humans around 2000 years ago, nearly all of the island's megafauna became extinct, including:
Starting c. 1500, a number of species became extinct upon human settlement of the islands, including:
One scientist estimates the extinction may be 10,000 times the background extinction rate (the average between mass extinction events).[3][4] Nevertheless, in earlier studies, most scientists predicted 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.[7] Numerous scientific studies—such as a 2004 report published in Nature,[8] 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:[9] "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."[10] Some of the human causes of the current extinctions include deforestation, hunting, pollution, climate change,[11] and the introduction of non-native species.
189 countries which are signatory to the Convention on Biological Diversity (Rio Accord) have committed to preparing a Biodiversity Action Plan, a first step at identifying specific endangered species and habitats, country by country.
Extinction of animals and plants caused by human actions may go as far back as the late Pleistocene, over 12,000 years BP, but there is no direct evidence for this theory and it is more likely abrupt climate change played a much higher role in the extinction of larger mammals.[12] Extinctions that are due to human activity (anthropogenic), particularly hypothesized future events, have also been labelled the anthropocene extinction.[13][14] The Anthropocene is a term introduced in 2000.
Recent extinctions described are well-documented,[12] but the nomenclature used varies. The term Anthropocene is a term that is used by few scientists,[12] and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.[15] 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.[16] 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. "[12]
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,[17] the study by Lyons et al., demonstrated conclusively that a hyperdisease was unlikely to have caused the extinction.[18] 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.[19] Most scientists favor abrupt climate climate change as the catalyst for the extinction of the mega-fauna at the end of the Pleistocene, but there are many who believe increased hunting from early modern humans also played a part. [20][21]
Millions of years before present
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