||It has been suggested that this article be merged with Quaternary extinction event. (Discuss) Proposed since January 2016.|
The Holocene extinction, otherwise referred to as the Sixth extinction or Anthropocene extinction, is a name proposed to describe the ongoing extinction event of species during the present Holocene epoch (since around 10,000 BCE) mainly due to human activity. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods. Although 875 extinctions occurring between 1500 and 2009 have been documented by the International Union for Conservation of Nature and Natural Resources, with widespread degradation of highly biodiverse habitats such as coral reefs and rainforest, as well as other areas, the vast majority are thought to be undocumented. According to the species-area theory and based on upper-bound estimating, the present rate of extinction may be up to 140,000 species per year, making it the greatest loss of biodiversity since the Cretaceous–Paleogene extinction event.
The Holocene extinction includes the disappearance of large land animals known as megafauna, starting between 9,000 and 13,000 years ago, the end of the last Ice Age. Megafauna outside of the African continent, that did not evolve alongside humans, proved highly sensitive to the introduction of new predation, and many died out shortly after early humans began spreading and hunting across the Earth (additionally, many African species have also gone extinct in the Holocene). The extinction of the mammoths, whose habits had maintained grasslands became birch forests without them. The new forest and the resulting forest fires may have induced climate change. Such disappearances might be the result of the proliferation of modern humans. These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event.
There is no general agreement on where the Holocene, or anthropogenic, extinction begins, and the Quaternary extinction event which includes climate change resulting in the end of the last ice age ends, or if they should be considered separate events at all. Some have suggested that anthropogenic extinctions may have begun as early as when the first modern humans spread out of Africa between 100,000 and 200,000 years ago, which is supported by rapid megafaunal extinction following recent human colonisation in Australia, New Zealand and Madagascar, in a similar way that any large, adaptable predator moving into a new ecosystem would. In many cases, it is suggested even minimal hunting pressure was enough to wipe out large fauna, particularly on geographically isolated islands. Only during the most recent parts of the extinction have plants also suffered large losses.
The ecology of Homo sapiens has been noted as being that of an unprecedented 'global superpredator' that regularly preys on the adults of other apex predators and has worldwide effects on food webs. Extinctions of species have occurred on every land mass and ocean, with many famous examples within Africa, Asia, Europe, Australia, North and South America, and on smaller islands. Overall, the Holocene extinction can be characterized by the human impact on the environment. The Holocene extinction continues into the 21st century, with overfishing, ocean acidification and the amphibian crisis being a few broader examples of an almost universal, cosmopolitan decline of biodiversity.
It has been suggested human activity has made the period following the mid-20th century different enough from the Holocene to consider it a new geological epoch, known as the Anthropocene, which will be considered for implementation into the timeline of Earth's history by the International Commission on Stratigraphy in 2016.
- 1 Human influence on extinction
- 2 Prehistoric extinctions
- 3 Extinctions into the Common Era
- 4 Recent extinctions - 1500 onwards
- 5 Contemporary crises
- 6 Lists of affected species
- 7 See also
- 8 References
- 9 Further reading
- 10 External links
Human influence on extinction
Extinction of animals, plants, and other organisms caused by human actions may go as far back as the late Pleistocene, over 12,000 years ago. There is evidence that abrupt climate change has especially played an enormous role in the extinction of larger mammals. However, while previous mass extinctions were due to natural environmental causes, research shows that wherever on Earth humans have migrated, other species have gone extinct, and human population growth, most prominently in the past two centuries, is regarded as one of the underlying causes of extinction. In terms of how humans have contributed, three major factors include the increased global concentration of greenhouse gases, affecting the global climate; oceanic devastation, such as through overfishing and contamination; and the modification and destruction of vast tracts of land and river systems around the world to meet solely human-centered ends (with 10 to 15 percent of Earth's land surface now used as urban-industrial or row-crop agricultural sites and 6 to 8 percent used as pastures), thus ruining the local ecosystems. Other, related human causes of the extinction event include deforestation, hunting, pollution, the introduction in various regions of non-native species, and the widespread transmission of infectious diseases. At present, the rate of extinction of species is estimated at 100 to 1,000 times higher than the "base" or historically typical rate of extinction (in terms of the natural evolution of the planet) and also the current rate of extinction is, therefore, 10 to 100 times higher than any of the previous mass extinctions in the history of Earth. It is also the only known mass extinction of plants.
The abundance of species extinctions considered anthropogenic, or due to human activity, have sometimes (especially when referring to hypothesized future events) been collectively called the "Anthropocene extinction". The Anthropocene is a term introduced in 2000. It is now widely accepted that a new geological epoch has begun, characterised by the most abrupt and widespread extinction of species since the Cretaceous–Paleogene extinction event 66 million years ago. 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. 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. Numerous scientific studies—such as a 2004 report published in Nature, 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.
The evidence of all previous extinctions is geological in nature, and shorter geological time scale is of the order of several hundred thousand to several million years. Even extinctions caused by instantaneous events such as the impact of the asteroid in Chicxulub, which is currently the best example, extend the equivalent of many human lives, due to complex ecological interactions that were triggered by the event.
Recent extinctions described are well-documented, but the nomenclature used varies. The term Anthropocene is a term that is used by few scientists, and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction. 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. 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."
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, a study by Lyons et al., demonstrated conclusively that a hyperdisease was unlikely to have caused the extinction. 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. Some scientists favor abrupt 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, with others even suggesting that the two interacted. In the Americas, a controversial explanation for the shift in climate is presented under the Younger Dryas impact hypothesis.
Megafauna was once found on every continent of the world and large islands such as New Zealand and Madagascar, but is now almost exclusively found on the continent of Africa, with notable comparisons on Australia and the islands previously mentioned experiences population crashes and trophic cascades shortly after the earliest human settlers. It has been suggested that the African megafauna survived as they evolved alongside humans. The timing of South American megafaunal extinction does not appear to correspond to human arrival, although the possibility of whether human activity at the time may have impacted the global climate enough to cause such an extinction has been suggested.
It has been noted, in the face of such evidence, Homo sapiens is unique in its ecology as an unprecedented 'global superpredator', regularly preying on large numbers of fully grown terrestrial and marine apex predators, and with a great deal of influence over food webs and climatic systems worldwide.
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Although significant debate exists as to how much human predation and indirect effects contributed to prehistoric extinctions, certain population crashes have been directly correlated with human arrival.
Australia was once home to a large assemblage of megafauna, with many parallels to those found on the African continent today. Australia's fauna is characterised by primarily marsupial mammals, and many reptiles and birds, all existing as giant forms until recently. Humans arrived on the continent very early, about 50,000 years ago. The extent human arrival contributed is controversial; climatic drying of Australia 40,000-60,000 years ago was an unlikely cause, as it was less severe in speed or magnitude than previous regional climate change which failed to kill off megafauna.
Due to the older timeframe and the soil chemistry on the continent, very little subfossil preservation evidence exists than elsewhere. However, continent-wide extinction of all genera weighing over 100 kilograms, and six of seven genera weighing between 45 and 100 kilograms occurred around 46,400 years ago (4,000 years after human arrival) and the fact that megafauna survived until a later date on the island of Tasmania following the establishment of a land bridge suggest direct hunting or anthropogenic ecosystem disruption such as fire-stick farming as likely causes. The first evidence of direct human predation leading to extinction in Australia was published in 2016.
- Dromornithidae, an entire family of giant birds. Though around the size of emus, they are actually more related to ducks and other waterfowl. Analysis of burned eggshells in Genyornis newtoni, which stood around 7 feet tall, suggested human consumption. As of yet, this is the most reliable direct evidence of human predation on Australian megafauna.
- Diprotodon, giant relatives of wombats
- Zygomaturus, a marsupial superficially resembling a rhinoceros
- Hulitherium, a large marsupial herbivore
- Phascolonus, a giant wombat
- Palorchestes azael, a marsupial "tapir"
- A highly diverse assemblage of kangaroos. These include giant species from several genus, including Macropus titan, Simosthenurus, Sthenurus and Protemnodon. Other unique kangaroo radiations include Procoptodon goliah, a hoof-toed giant short-faced kangaroo, and Propleopus oscillans, an omnivorous kangaroo
- Wonambi, a five-to-six-metre-long Australian constrictor snake
- Thylacoleo carnifex, a lioness-sized marsupial carnivore
- Varanus priscus, a giant predatory monitor lizard
- Zaglossus hacketti, a giant species of echidna
- Quinkana, a five-to-six metre-long predatory terrestrial crocodile
North and South America
There has been a debate as to the extent to which the disappearance of megafauna at the end of the last glacial period can be attributed to human activities by hunting, or even by slaughter of prey populations. Discoveries at Monte Verde in South America and at Meadowcroft Rock Shelter in Pennsylvania have caused a controversy regarding the Clovis culture. There likely would have been human settlements prior to the Clovis Culture, and the history of humans in the Americas may extend back many thousands of years before the Clovis culture. The amount of correlation between human arrival and megafauna extinction is still being debated: for example, in Wrangel Island in Siberia the extinction of dwarf woolly mammoths (approximately 2000 BCE) did not coincide with the arrival of humans, nor did megafaunal mass extinction on the South American continent, although it has been suggested climate changed induced by anthropogenic effects elsewhere in the world may have contributed.
Comparisons are sometimes made between recent extinctions (approximately since the industrial revolution) and 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. We know that humans of this era actively hunted the mammoth and the mastodon but it is not known if this hunting was the cause of the subsequent massive ecological changes, widespread extinctions and climate changes.
The ecosystems encountered by the first Americans had not been exposed to human interaction, and may have been far less resilient to human made changes than the ecosystems encountered by industrial era humans. Therefore, the actions of the Clovis people, despite seeming insignificant by today's standards could indeed have had a profound effect on the ecosystems and wild life which was entirely unused to human influence.
The following species, among many others, became extinct in this period.
- Doedicurus, a giant armadillo
- American cheetah
- American lion
- Holochilus primigenus
- Pygmy mammoth and woolly mammoth
- Smilodon, sabre toothed cats
Human arrival around 6,000 years ago is correlated with the extinction of many species. Examples include:
- Many different genera of ground and arboreal sloths across all islands. These sloths were generally smaller than those found on the South American continent. Megalocnus were the largest genus at up to 90 kg, Acratocnus were medium-sized relatives of modern two-toed sloths endemic to Cuba, Imagocnus also of Cuba, Neocnus and many others.
- Giant hutias
- Cuban coney
- Cuban giant owl
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. It is currently estimated that among the bird species of the Pacific some 2000 species have gone extinct since the arrival of humans, representing a 20% drop in the biodiversity of birds worldwide. Among the extinctions were:
- Sylviornis, a giant galliform bird from New Caledonia
- Mekosuchine crocodiles from New Caledonia, Fiji and Samoa.
- Meiolaniid turtles on Lord Howe Island and New Caledonia
- "Gavialis" papuensis, a marine crocodilian from the Solomon Islands.
- Pygmy hippos of Cyprus (Phanourios minutus), Crete (Hippopotamus creutzburgi), Malta (H. melitensis) and Sicily (H. pentlandi)
- Balearic Islands cave goat (Myotragus balearicus) of Majorca and Minorca
- A diverse assemblage of dwarf elephants of several islands, including Cyprus (Elephas cypriotes), Sicily, Malta (E. falconeri) and Crete (Mammuthus creticus)
- Giant swan (Cygnus falconeri) of Malta
- Giant dormice: Minorcan giant dormouse, Majorcan giant dormouse
- Sardinian pika of Sardinia and Corsica
Extinctions into the Common Era
More recent settlement of isolated land masses where megafauna continued to survive almost immediately resulted in their extinction. Calculations suggest this occurred even if only a small number of animals were hunted. It has been suggested this contemporary evidence supports the theory that humans were capable of causing or at least contributing to the extinctions of the Quaternary extinction event.
The first settlers are thought to have arrived in the islands between 300 and 800 CE, with European arrival in the 16th century. Hawaii is notable for its endemism of plants, birds, insects, mollusks and fish; 30% of its organisms are endemic. Many of its species are endangered or have gone extinct, primarily due to accidentally introduced species and livestock grazing. Over 40% of its bird species have gone extinct, and it is the location of 75% of extinctions in the United States.
Extinction has increased in Hawaii over the last 200 years and is relatively well documented, with extinctions among native snails used as estimates for global extinction rates.
- The moa-nalos, grazing ducks from Hawaii.
- The nēnē-nui, or woodwalking goose, a large species of goose that once inhabited the island of Maui.
- Kauaʻi finch, a large finch
Indian Ocean Islands
Starting circa 1500 years ago, a number of species became extinct upon human settlement of the islands, including:
- Several species of giant tortoise on the Seychelles and Mascarene Islands, including Cylindraspis and Meiolania platyceps
- Aldabrachampsus, a Crocodyliform found on the Aldabra Atoll
Within 500 years of the arrival of humans between 2,500-2,000 years ago, nearly all of Madagascar's distinct, endemic and geographically isolated megafauna became extinct. The largest animals, of more than 150 kg, were extincted very shortly after the first human arrival, with large and medium-sized species dying out after prolonged hunting pressure from an expanding human population moving into more remote regions of the island around 1000 years ago. Smaller fauna experienced initial increases due to decreased competition, and then subsequent declines over the last 500 years. All fauna weighing over 10 kg died out. The primary reasons for this are human hunting and habitat loss from early aridification, both of persist and threaten Madagascar's remaining taxa today.
- Eight or more species of elephant birds, giant flightless ratites in the genera Aepyornis and Mullerornis.
- 17 species of lemur, known as giant, subfossil lemurs. Some of these lemurs typically weighed over 150 kg, and fossils have provided evidence of human butchery on many species.
- Giant aye-aye (Daubentonia robusta)
- Sloth lemurs, including chimpanzee-sized Palaeopropithecus and gorilla-sized Archaeoindris
- Koala lemurs (Megaladapis), a koala-like, orangutan-sized arboreal lemur
- Monkey lemurs, most terrestrial of lemurs, often compared to baboons or macaques.
- Pachylemur, a larger, more robust genus of ruffed lemurs
- Giant fossa
- Voay, a terrestrial giant dwarf crocodile
- Plesiorycteropus, a genus containing two species of superficially Aardvark-like digging mammal unlike anything alive today
- Three species of Malagasy hippopotamus
- Malagasy crowned eagle (Stephanoaetus mahery), a giant bird of prey
- Local giant tortoises of genus Geochelone, including Aldabrachelys abrupta and Aldabrachelys grandidieri. The latter were important seed dispersers for endemic baobab trees.
Recent extinctions - 1500 onwards
One scientist estimates the current extinction rate may be 10,000 times the background extinction rate. Nevertheless, most scientists predict a much lower extinction rate than this outlying estimate. Stuart Pimm stated "the current rate of species extinction is about 100 times the natural rate" for plants. Mass extinctions are characterized by the loss of at least 75% of species within a geologically short period of time.
In a pair of studies published in 2015, extrapolation from observed extinction of Hawaiian snails led to the conclusion that 7% of all species on Earth may have been lost already.
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 (such as the Père David's deer, Hawaiian crow) and by marginal survivals of highly publicized megafauna that are ecologically extinct (such as the giant panda, Sumatran rhinoceros, North American black-footed ferret). However, the Holocene can also be characterisied by widespread extinctions among arthropods, widespread local extinctions of populations of species that still exist elsewhere (such as the extinction of gray whales in the Atlantic and of the leatherback sea turtle in Malaysia) and by universal declines in range and population of various animal and plant species throughout all of the world.
The IUCN characterises 'recent' extinction as those that have occurred past the cut-off point of 1500. The extinct species listed below are not comprehensive, but are some of the most famous examples.
New Zealand is characterised by its geographic isolation and island biogeography, and had been isolated from mainland Australia for 80 million years. It was one of the last large land masses to be colonised by humans. The arrival of Polynesian settlers circa 13th century resulted in the extinction of all of the islands megafaunal birds. Pressure from human hunting and introduced species such as possums and rats had a devastating effect on native birds, many of which had adapted flightlessness and ground nesting habits in response to having no extant endemic mammalian predators. Further extinctions have occurred since European settlement in the mid-19th century, and subsequent development.
Extinctions include, among many others:
- Eleven species of moa, giant flightless ratites. The last moa went extinct around the 1500s, although accounts suggest some may have survived until more recently. It has been suggested even moderate hunting pressure was enough to drive moa across the islands to extinction in less than 200 years.
- The giant Haast's eagle, Harpagornis
- Two species of giant flightless predatory adzebills.
- Finsch's duck, a large, flightless duck
Other notable recent extinctions
Some examples of modern extinctions of "charismatic" mammal fauna include:
- Aurochs (1627), a wild cow that was domesticated to form modern cattle.
- Steller's sea cow (1768), a large sirenian driven to extinction across its prehistoric range across the North Pacific by hunting. The last populations, reduced to the Commander Islands, were driven to extinction 27 years after their discovery by Europeans in 1741 (where they may have numbered at 2000) after heavy hunting.
- Sardinian pika (1774) primitive lagomorph native to the Mediterranean islands of Sardinia and Corsica
- Bluebuck, a species of antelope. Despite already being uncommon by the time of European discovery, habitat conversion for agriculture and hunting resulted in its extinction by 1800.
- Atlas bear (1870s)
- Falkland Islands wolf (1876)
- Quagga (1883), zebra subspecies, Southeast Africa. Recent attempts have been made by the Quagga Projectto selectively breed Burchell's zebras to susuperficially semble quaggas.
- Tarpan, a European wild horse. Although extinct in the wild by 1890, the last captive animal died in 1909.
- Thylacine (1936) or Tasmanian tiger, Thylacinus cynocephalus, a marsupial carnivore prosecuted by farmers and the government for predating on livestock
- Caribbean monk seal (1950s)
- Japanese sea lion (1970s)
- Pyrenean ibex (2000). Attempts were made to clone the species shortly after its extinction, and despite brief success the only surviving foetus died after 7 minutes.
- Yangtze dolphin, extinct 2006
- The closely related Bali tiger (1937) and Javan tiger (1970s)
- Eastern cougar (2011) a subspecies of North American cougar
- Western black rhinoceros (2011), a subspecies
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:
- Many species of birds on the Mascarene Islands, including the giant flightless pigeons known as the dodo of Mauritius (1662) and the Rodrigues solitaire (1778) and the unrelated Réunion solitaire, which was a flightless ibis (early 1800s)
- Great auk (1852) once highly abundant flightless auk around the North Atlantic
- Passenger pigeons (1914) of North America, once so abundant that accounts suggest their flocks took days to pass
- The Carolina parakeet (1918) of the American southeast
- Ivory-billed woodpecker (2000)
- Kauaʻi ʻōʻō
- All members of the group Nukupu‘u. Two species went extinct in the 1990s.
- All members of the finch genus Akialoa.
- Poʻouli, a single species of Hawaiian honeycreeper within its own genus.
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Peter Raven, past president of the American Association for the Advancement of Science (AAAS), states in the foreword to their publication AAAS Atlas of Population and Environment: "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."
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.
The decline of amphibian populations has also been identified as an indicator of environmental degradation. As well as habitat loss, introduced predators and pollution, Chytridiomycosis, a fungal infection thought to have been accidentally spread by human travel, has caused severe population drops of several species of frogs, including (among many others) the extinction of the golden toad in Costa Rica and the Gastric-brooding frog in Australia. Many other amphibian species now face extinction, including the reduction of Rabb's fringe-limbed treefrog to an endling, and the extinction of the Panamanian golden frog in the wild. Chytrid fungus has spread across Australia, New Zealand, Central America and Africa, including countries with high amphibian diversity such as cloud forests in Honduras and Madagascar. Amphibians are now the most endangered vertebrate group, having existed for more than 300 million years through three other mass extinctions.
Mass bat deaths
Millions of bats in the US have been dying off since 2012 due to a fungal infection spread from European bats, which appear to be immune. Population drops have been as great as 90% within five years, and extinction of at least one bat species is predicted. There is currently no form of treatment, and such declines have been described as "unprecedented" in bat evolutionary history by Alan Hicks of the New York State Department of Environmental Conservation.
Global warming is widely accepted as being a contributor to extinction worldwide, in a similar way that previous extinction events have generally included a rapid change in global climate and meteorology. It is also expected to disrupt sex ratios in many reptiles which have temperature-dependent sex determination.
Degradation of marine habitats
Rising levels of carbon dioxide are resulting in influx of this gas into the ocean, increasing its acidity. Marine organisms which possess Calcium Carbonate shells or exoskeletons experience physiological pressure as the carbonate reacts with acid. This is already resulting in coral bleaching on various coral reefs worldwide, which provide valuable habitat for very high biodiversity. Marine gastropods, bivalves and other invertebrates are also affected, as are any organisms that feed on them.
Fishing has had a devastating effect on marine organism populations for several centuries even before the explosion of destructive and highly effective fishing practices like trawling. Humans are unique among predators in that they regularly predate on other adult apex predators, particularly in marine environments; bluefin tuna and various sharks in particular are particularly vulnerable to predation pressure from human fishing.
The term pollinator decline refers to the reduction in abundance of insect and other animal pollinators in many ecosystems worldwide beginning at the end of the twentieth century, and continuing into the present day.
Lists of affected species
- Effects of global warming
- Extinction risk from global warming
- List of extinct animals
- List of extinct plants
- Late Quaternary prehistoric birds
- Timeline of extinctions
- Decline in amphibian populations
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