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Holocene extinction event |
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 100,000 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.
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The ongoing extinction event seems more outstanding if we follow tradition and separate the recent extinction (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.
c. CE 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 arrivial of humans (Steadman 1995). Among the extinctions were:
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:
Starting c. 1500 CE, a number of species became extinct upon human settlement of the islands, including:
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Wikinews has related news: Largest mass extinction in 65 million years underway, scientists say |
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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:
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:
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
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.
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