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Friday, February 20, 2015

Holocene extinction


From Wikipedia, the free encyclopedia

The dodo, a flightless 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 quagga became extinct in 1883.
The passenger pigeon became extinct in 1914.
The Mexican grizzly bear became extinct in 1964.
The Caribbean monk seal was officially declared extinct in 2008.

The Holocene extinction, sometimes called the Sixth Extinction, is a name proposed to describe the extinction event of species that has been taking place 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,[1] the vast majority are 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.[2]

The Holocene extinction includes the disappearance of large mammals known as megafauna, starting between 9,000 and 13,000 years ago, the end of the last Ice Age. This may have been due to the extinction of the mammoths whose habits had maintained grasslands which became birch forests without them.[3] The new forest and the resulting forest fires may have induced climate change.[3] Such disappearances might be the result of the proliferation of modern humans which led to climate change. These extinctions, occurring near the Pleistocene–Holocene boundary, are sometimes referred to as the Quaternary extinction event. The Holocene extinction continues into the 21st century.

There is no general agreement on whether to consider this as merely part of the Quaternary extinction event, or just a result of human-caused changes.[3][4] Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction can be characterized by the human impact on the environment.

Prehistoric extinctions

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, directly, by hunting, or indirectly, by slaughter[clarification needed] of prey populations. Discoveries at Monte Verde in South America and at Meadowcroft Rock Shelter in Pennsylvania have caused a controversy[5] regarding the Clovis Culture. There likely 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.[5] There is no strong correlation between human arrival and megafauna extinction: for example in Wrangel Island in Siberia the extinction of midget Mammoths (approximately 1000 BCE)[6] did not coincide with the arrival of humans.

The ongoing extinction seems more outstanding[clarification needed] in view of the apparent separation[clarification needed] 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[7] but it is not known if this hunting was the cause of the subsequent massive ecological changes, widespread extinctions and climate changes.[3][4] The ecosystems encountered by the first Americans had not been exposed to human interaction and were far less resilient to human made changes than the ecosystems encountered by industrial era humans, those environments seasoned as they were, having been exposed to over 10,000 years of human interaction. Therefore the actions of the Clovis people and likewise[clarification needed], 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.

New Zealand

Circa 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.[8] It is currently estimated that among the bird species of the Pacific some 2000 species have gone extinct since the arrival of humans.[9] 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 2,000 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 extinctions

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.[10] Stuart Pimm stated "the current rate of species extinction is about 100 times the natural rate" for plants.[11] Mass extinctions are characterized by the loss of at least 75% of species within a geologically short period of time.[12][13][14]

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:
The decline of amphibian populations has also been identified as an indicator of environmental degradation.

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:[16] "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."[17]

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 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.

Various species are predicted to go extinct in the near future.[18][19][20][21]

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.[22] 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 this Holocene extinction event.[23] In terms of how humans have contributed to this mass extinction, 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.[24][25] Other, related human causes of the extinction event include deforestation, hunting, pollution,[26] the introduction in various regions of non-native species, and the widepsread 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)[27] 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.[citation needed] On the other hand, this extinction concerns a large number of plants, different from previous extinctions.

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".[28][29] The Anthropocene is a term introduced in 2000. Most biologists believe that we are at the beginning of an anthropogenic mass extinction that is accelerating at a large rate.[citation needed] 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.[30] Numerous scientific studies—such as a 2004 report published in Nature,[31] 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 are triggered by the event.[citation needed]

Recent extinctions described are well-documented,[22] but the nomenclature used varies. The term Anthropocene is a term that is used by few scientists,[22] and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.[32] 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.[33] 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."[22]

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,[34] the study by Lyons et al., demonstrated conclusively that a hyperdisease was unlikely to have caused the extinction.[35] 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.[36] 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.[37][38]

De-extinction

De-extinction is the process of creating an organism, which is a member of or resembles an extinct species, or a breeding population of such organisms. Cloning is the most widely proposed method, although selective breeding has also been proposed.
Several species that have gone extinct during the holocene period have been proposed for de-extinction. These include: passenger pigeon, moa, heath hen, dodo and woolly mammoth.

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Endangered species


From Wikipedia, the free encyclopedia

Conservation status
Bufo periglenes, the Golden Toad, was last recorded on May 15, 1989
Extinct
Threatened
Lower Risk
Other categories
Related topics
IUCN Red List category abbreviations (version 3.1, 2001)

    An Endangered (EN) species is a species which has been categorized by the International Union for Conservation of Nature (IUCN) Red List as likely to become extinct. "Endangered" is the second most severe conservation status for wild populations in the IUCN's schema after Critically Endangered (CR).

    In 2012, the IUCN Red List featured 3079 animal and 2655 plant species as Endangered (EN) worldwide.[1] The figures for 1998 were, respectively, 1102 and 1197.[citation needed]

    Many nations have laws that protect conservation-reliant species: for example, forbidding hunting, restricting land development or creating preserves. Population numbers, trends and species' conservation status can be found in the lists of organisms by population.

    Conservation status

    The conservation status of a species indicates the likelihood that it will become extinct. Many factors are considered when assessing the conservation status of a species; e.g., such statistics as the number remaining, the overall increase or decrease in the population over time, breeding success rates, or known threats.[2] The IUCN Red List of Threatened Species is the best-known worldwide conservation status listing and ranking system.[3]

    Over 40% of the world's species are estimated to be at risk of extinction.[4] Internationally, 199 countries have signed an accord to create Biodiversity Action Plans that will protect endangered and other threatened species. In the United States, such plans are usually called Species Recovery Plans.[citation needed]

    IUCN Red List


    The Siberian tiger is an Endangered (EN) tiger subspecies. Three tiger subspecies are already extinct (see List of carnivorans by population).[5]

    Though labelled a list, the IUCN Red List is a system of assessing the global conservation status of species that includes "Data Deficient" (DD) species – species for which more data and assessment is required before their status may be determined – as well species comprehensively assessed by the IUCN's species assessment process. Those species of "Near Threatened" (NT) and "Least Concern" (LC) status have been assessed and found to have relatively robust and healthy popoulations, though these may be in decline. Unlike their more general use elsewhere, the List uses the terms "endangered species" and "threatened species" with particular meanings: "Endangered" (EN) species lie between "Vulnerable" (VU) and "Critically Endangered" (CR) species, while "Threatened" species are those species determined to be Vulnerable, Endangered or Critically Endangered.

    The IUCN categories, with examples of animals classified by them, include:
    Extinct (EX) 
    Extinct in the wild (EW) 
    Captive individuals survive, but there is no free-living, natural population.
    Critically endangered (CR) 
    Faces an extremely high risk of extinction in the immediate future.
    Endangered (EN) 
    Faces a very high risk of extinction in the near future.
    Vulnerable (VU) 
    Faces a high risk of extinction in the medium term.
    Near-threatened (NT) 
    May be considered threatened in the near future.
    Least concern (LC) 
    No immediate threat to species' survival.

      United States

      Endangered Species Act


      "Endangered" in relation to "threatened" under the ESA.

      Under the Endangered Species Act in the United States, species may be listed as "endangered" or "threatened". The Salt Creek tiger beetle (Cicindela nevadica lincolniana) is an example of an endangered subspecies protected under the ESA. The US Fish and Wildlife Service as well as the National Marine Fisheries Service are held responsible for classifying and protecting endangered species, and adding a particular species to the list can be a long, controversial process (Wilcove & Master, 2008, p. 414).

      Some endangered species laws are controversial. Typical areas of controversy include: criteria for placing a species on the endangered species list and criteria for removing a species from the list once its population has recovered; whether restrictions on land development constitute a "taking" of land by the government; the related question of whether private landowners should be compensated for the loss of uses of their lands; and obtaining reasonable exceptions to protection laws. Also lobbying from hunters and various industries like the petroleum industry, construction industry, and logging, has been an obstacle in establishing endangered species laws.

      The Bush administration lifted a policy that required federal officials consult a wildlife expert before taking actions that could damage endangered species. Under the Obama administration, this policy has been reinstated.[7]

      Being listed as an endangered species can have negative effect since it could make a species more desirable for collectors and poachers.[8] This effect is potentially reducible, such as in China where commercially farmed turtles may be reducing some of the pressure to poach endangered species.[9]

      Another problem with the listing species is its effect of inciting the use of the "shoot, shovel, and shut-up" method of clearing endangered species from an area of land. Some landowners currently may perceive a diminution in value for their land after finding an endangered animal on it. They have allegedly opted to silently kill and bury the animals or destroy habitat, thus removing the problem from their land, but at the same time further reducing the population of an endangered species.[10] The effectiveness of the Endangered Species Act – which coined the term "endangered species" – has been questioned by business advocacy groups and their publications but is nevertheless widely recognized by wildlife scientists who work with the species as an effective recovery tool. Nineteen species have been delisted and recovered[11] and 93% of listed species in the northeastern United States have a recovering or stable population.[12]

      Currently, 1,556 known species in the world have been identified as near extinction or endangered and are under protection by government law. This approximation, however, does not take into consideration the number of species threatened with endangerment that are not included under the protection of such laws as the Endangered Species Act. According to NatureServe's global conservation status, approximately thirteen percent of vertebrates (excluding marine fish), seventeen percent of vascular plants, and six to eighteen percent of fungi are considered imperiled.[13]:415 Thus, in total, between seven and eighteen percent of the United States' known animals, fungi and plants are near extinction.[13]:416 This total is substantially more than the number of species protected in the United States under the Endangered Species Act.

      Over-hunting

      Over-hunting and over-fishing have been a problem ever since mankind started to hunt. Of those species whose extinction is known to have resulted from over-hunting, the dodo, passenger pigeon, great auk, Tasmanian tiger and Steller's sea cow are among the more well-known; the bald eagle, grizzly bear, American bison, timber wolf and sea turtle, meanwhile, have been hunted to near-extinction. Many began as food sources seen as necessary for survival but became the target of sport. A present-day example of the over-hunting of a species can be seen in the oceans as populations of certain whales have been greatly reduced. Large whales like the blue whale, bowhead whale, finback whale, gray whale, sperm whale and humpback whale are some of the eight whales which are currently still included on the Endangered Species List. Actions have been taken to try to reduce whaling and increase population sizes, including prohibiting all whaling in United States waters, the formation of the CITES treaty which protects all whales, along with the formation of the International Whaling Commission (IWC). But even though all of these movements have been put in place, countries such as Japan continue to hunt and harvest whales under the claim of "scientific purposes".[14] Over-hunting, climatic change and habitat loss [? leads in landing species in endangered species list] and could mean that extinction rates could increase to a large extent in the future.

      Invasive species

      The introduction of non indigenous species to an area can disrupt the ecosystem to such an extent that native species become endangered. Such introductions may be termed alien or invasive species. In some cases the invasive species compete with the native species for food or prey on the natives. In other cases a stable ecological balance may be upset by predation or other causes leading to unexpected species decline. New species may also carry diseases to which the native species have no resistance.[15]

      Conservation


      The dhole, Asia's most endangered top predator, is on the edge of extinction.

      Captive breeding

      Captive breeding is the process of breeding rare or endangered species in human controlled environments with restricted settings, such as wildlife preserves, zoos and other conservation facilities. Captive breeding is meant to save species from extinction and so stabilize the population of the species that it will not disappear.[16]
      This technique has worked for many species for some time, with probably the oldest known such instances of captive mating being attributed to menageries of European and Asian rulers, an example being the Père David's deer. However, captive breeding techniques are usually difficult to implement for such highly mobile species as some migratory birds (e.g. cranes) and fishes (e.g. hilsa). Additionally, if the captive breeding population is too small, then inbreeding may occur due to a reduced gene pool and reduce immunity.

      Private farming

      Whereas poaching substantially reduces endangered animal populations, legal, for-profit, private farming does the opposite. It has substantially increased the populations of the southern black rhinoceros and southern white rhinoceros. Dr Richard Emslie, a scientific officer at the IUCN, said of such programs, "Effective law enforcement has become much easier now that the animals are largely privately owned... We have been able to bring local communities into the conservation programmes. There are increasingly strong economic incentives attached to looking after rhinos rather than simply poaching: from Eco-tourism or selling them on for a profit. So many owners are keeping them secure. The private sector has been key to helping our work."[17]

      Conservation experts view the effect of China's turtle farming on the wild turtle populations of China and South-Eastern Asia – many of which are endangered – as "poorly understood".[18] Although they commend the gradual replacement of turtles caught wild with farm-raised turtles in the marketplace – the percentage of farm-raised individuals in the "visible" trade grew from around 30% in 2000 to around 70% in 2007[19] – they worry that many wild animals are caught to provide farmers with breeding stock. The conservation expert Peter Paul van Dijk noted that turtle farmers often believe that animals caught wild are superior breeding stock. Turtle farmers may, therefore, seek and catch the last remaining wild specimens of some endangered turtle species.[19]

      In 2009, researchers in Australia managed to coax southern bluefin tuna to breed in landlocked tanks, raising the possibility that fish farming may be able to save the species from overfishing.[20]

      Countries with endangered animals

      Around the world hundreds of thousands of species are lost to extinction, many of them only discovered as remains, after they are gone. Thus, not only biological variability, but also genetic diversity, and perhaps sources of livelihood for future generations are lost. An endangered species is a species that may become extinct in the near future. Throughout history, millions of species have disappeared due to natural processes. In the past 300 years, however, humans have increased the rate of extinction.

      For some plant and animal species, living seems to be a daily hazard. And humans seem to pose the biggest threat. Ecological disasters, hunting/poaching, deforestation and other consequences of human action causes damage to the food chain, breeding grounds, and habitat.

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