In Biology and ecology, the extinction is the total disappearance of a species or groups Taxons, thus reducing the Biodiversité. The moment of the extinction is generally regarded as being the death of the last individual of the species (although the capacity to be procreated and repopulate themselves was lost before).

Through the evolution, new species appear by the process of the Spéciation - where of new varieties of organizations emergent and develop when they are able to find and exploit a ecological Niche - and species disappear when they are not able any more to survive under conditions changeantes or against a higher competition. Typically, a species dies out in the 10 million years after its first appearance, although certain species, called fossil alive, survive practically unchanged during hundreds of million years. Only 1/1000 of the species having existed are still alive today.

Before the propagation of the man on all planet, the rate of extinction was invariably weak, the extinctions of mass being relatively rare events. Starting roughly 100.000 years ago and coinciding with the growth of the number and the distribution of the men, the extinction of the species increased ata rate without precedent since large the Extinction of the Cretaceous. This phenomenon is known under the name of Extinction of Holocene the and represents the sixth massive extinction. Certain experts estimate that more half of the alive species today can die out from here 2100.

Definitions

A species disappears when the last member of this species dies. The extinction thus becomes a certainty when there are no more surviving individuals able to reproduce and to create a new generation. A species can thus become functionally extinct , when only a handle of individuals survive but are unable to reproduce because of a low health, age or of a scattered distribution on a great extent, or because of a lack of individuals of the two sexes (for the species with sexuée reproduction) or for other reasons.

To establish the extinction (or pseudoextinction, to see following chapter) of a species requires a clear definition of this species. If she is declared extinct, the species in question must be identifiable in a single way, differentiated well from its ancestors, species downward or close. The extinction of a species (or replacement by a downward species) plays a key function on the assumption of the punctuated balance of Stephen Jay Gould and Niles Eldredge.

In ecology, the term extinction is often used informellement in reference to the phenomenon of local extinction (or eradication), in which a species ceases existing in a zone of study given but saw still elsewhere. The local extinctions can be followed by a reintroduction of the species thanks to individuals of other areas.

The extinction of the wild population of a species can have repercussions, in particular to cause additional extinctions. This is called “extinction in chain” or “coextinction”.

Pseudoextinction

An extinct species can or not have downward species. A species girl which evolved/moved since a species relationship carries the majority of the genetic Information of the species relationship, and even if this one dies out, the species girl can continue to exist or not to survive the extinction of its species relationship. The extinction of a species relationship for which one or more species girls or subspecies are always alive is thus called pseudoextinction .

A pseudoextinction is difficult to show unless there exists a strong chain of evidence binding a species alive to the members of a preexistent species. For example, it is sometimes constant that the Hyracotherium disappeared, which was an old animal similar to the Cheval, is pseudoéteint rather than extinct, because there are several alive species of the kind Equus, including the zebras and the asses. However, as the fossil species do not leave trace of genetic material, it is impossible to say if Hyracotherium evolved to the species of modern horses or simply advanced since a common ancestor with the modern horse. The pseudoextinction is simpler to show for more important taxonomic groups. It is known as that the dinosaurs are pseudoéteints, because some their descendants, the birds, exist still today.

Reappearance of species

Because the surface of distribution of a species can be very wide, to determine the moment of its extinction appears difficult and is usually made retrospectively. This difficulty leads to phenomena the such taxon of Lazare in whom a species supposed extinct “reappears” suddenly (typically in a fossil recording) after one period of apparent absence.

Species considered as " éteintes" , for lack of individuals observed during several years or decades, can thus be redécouvertes, the such Pic with nozzle ivory, the Petaurus gracilis , the Takahé or the Fuligule of Madagascar.

However, great organizations of conservation as UICN consider that these species are generally always threatened to disappear, the number of individuals observed being weak or at a stage close to the incapacity to renew the generations. In spite of that, certain species could live without being observed several decades, the such potorou of Gilbert, supposed extinct during 120 years.

Causes

Several causes can contribute directly or indirectly to the extinction of a species or a group of species. “In the same way that each species is single, each extinction is also… the causes of each one of them are varied - certain subtle and complex, other obvious and simple ones”.

More simply, any species inapt for to survive or to reproduce in its environment, and incompetent to move until a new environment where it can do it, dies and dies out.

A species not presenting normally a risk of extinction can disappear suddenly at the time of particularly serious events, as when a pollution returns the whole of its intolerable habitat; contrary, the phenomenon of extinction can proceed gradually on thousands or million years, for example when a species gradually loses the advantage in the competition for food vis-a-vis better adapted species.

In its work Extinction: Bad Genoa gold Bad Luck ( " Extinction: bad genes or bad chance" ), the paleontologist David Raup examines the importance of the genetic factors and environmental to cause the extinctions, and compares this topic with the debate " innate against acquis". is able to reduce this diversity significantly by strongly limiting the number of reproductive individuals and returns the more frequent Consanguinité. The most extreme example of the bottleneck of population is the effect founder, which can involve a fast Spéciation.

Destruction of the habitat

The destruction of the habitat of a species can deteriorate the adaptive landscape at a point such as the species is not more able to survive it and thus dies out. That can arrive by direct effects like pollution of the environment, or indirectly, by the limitation of the capacity of a species to remain effective in the competition for the natural resources or against of new concurrent species.

The degradation of the habitat by toxicity can put an end to a species very quickly, by killing all the members by contamination or while them making sterile. That can occur over long periods, on low levels of toxicity, affecting the lifespan, the capacities of reproduction or competitiveness.

Degradation can also take the form of a physical destruction of the habitats, having from time immemorial existed, but with a width much more important in particular since the Industrial revolution. A famous example is the destruction of the wet tropical forests and its replacement by Pâturage S, which reduced thus considerably the populations of Orang-outan in Asia; the destruction of the dense forest involves the elimination of the infrastructure necessary to the life of many species. For example, a fern needs much shade to protect itself from the direct light from the sun. It cannot survive without a forest to shelter it. Another case, destruction of the ocean floor by the trawling of sea-beds, the drainage of the wetlands for sylviculture or agriculture, etc

Resources drops some where the presence of new species in competition often accompanies degradation by the habitat. The Climate warming made it possible certain species to extend their territory, bringing a nondesired competition with the species which occupied already this zone. Sometimes these new candidates are the predatory ones and affect the species preys, or these new arrivals are in strong competition with the local species for natural resources in limited quantity. The vital resources such as water and food can also be limited, driving to the extinction.

Predation, competition and disease

The men transported animals and plants of one corner to the other of the world since thousands of years, sometimes deliberately (e.g. cattle unloaded on the islands and used like food) and sometimes accidentally (e.g. rats escaping from a boat). In the majority of the cases, such introductions are without success, but when a species succeeds in colonizing a territory (it becomes a invasive Espèce then), the consequences can be catastrophic.

The invasive species can affect the native species by eating them, entering in competition with them, by introducing Pathogène S or Parasite S which makes them sick or kills them, or indirectly by degrading their habitat.

The human populations can also act like the predatory invasive ones. According to the assumption of the prehistoric extermination, the rapid extinction of the Mégafaune in zones like New Zealand, Australia, Madagascar and Hawaii result from a sudden introduction the human ones into environments filled of animals which had never seen some before and were thus completely unsuited to their techniques of predation. Overexploitation by hunting can lead to the total disappearance of a species: it was the case of the dodo or the large mammals disappeared during the last millenia.

Nowadays, the growth of the international exchanges increases the extension risk of invasive species. In order to avoid this phenomenon, of customs controls at the borders are carried out, particularly in the airports.

Coextinction

See also: Coextinction

The coextinction refers to the loss of a species due to the disappearance of another species, for example, the extinction of parasitic insects after the extinction of their hosts. A coextinction can also occur when a plant specie loses its principal pollinating species, or when a predator does not have any more a prey. According to Lian Pih Koh, researcher in ecology and biology of the evolution at the National university of Singapore: Species coextinction has demonstration off the interconnectedness off organisms in complex ecosystems… While coextinction may not important Be the most causes off species extinctions, it is certainly year insidious one.
the coextinction of species is a manifestation of the interconnection of organizations in complex ecosystems… Although the coextinction can not be the most important cause of extinction of the species, it is certainly an insidious cause.

Massive extinctions

See also: massive Extinction

There were at least five great extinctions of mass during the history of the life on Earth, spreading out of -500 million years (Ordovicien) to -65 My (Crétacé), during which many species disappeared in one relatively short period of time (on a geological time scale).

In the chronological order:

  • Fine of the Ordovicien (- 440 My);
  • Fine of Dévonien (- 365 My);
  • Fine of Permian the (- 225 My);
  • Fin of the Sorted ic (- 210 My);
  • Fine of the Cretaceous (- 65 My): extinction of the Dinosaur S.

Massive extinction of the modern time

See also: Extinction of Holocene the

According to a survey of 1998 carried out near 400 biologists by the American Natural history museum of natural history of New York, nearly 70% of the biologists think that we are currently at the beginning of an extinction of mass caused by the man, known as a Extinction of Holocene the. In this survey, the same proportion of questioned people were of agreement with the prediction as up to 20% of all the alive populations could die out from here about thirty years (in 2028). The biologist Edward Osborne Wilson estimated into 2002 who if the current rate of destruction of the biosphere by the man were maintained, the half of all the species in life on Earth would be extinct within 100 years. In a more significant way, the rate of extinction of species at present is considered between 100 and 1000 times higher than the average rate of extinction than knew up to now the history of the evolution of the life on Earth, and is considered at 10 to 100 times faster than any extinction of preceding mass.

In 2004, a study published in Nature realized under the direction of Chris Thomas and based on a sample of areas covering 20% of terrestrial surface shows that the climate changes will involve the loss from 15 to 37% of the alive species from here 2050, according to the scenarios. That is to say a rate/rhythm exceeding very largely the geological time scale; what announces the sixième crisis of massive Extinction of the species that the Earth knew (the preceding ones being listed in preamble), this time for reasons Anthropique S.

According to the world Union for the conservation, 784 extinctions were recorded since the year 1500, the selected arbitrary date to define the extinctions of the modern time, although many other extinctions could pass unperceived.

Evolution of scientific comprehension

In the years 1800 when the phenomenon of extinction was the first time described, the idea even of extinction was alarming for the partisans of the Large chain of the life, a theological position which did not admit the possibility of the existence of " links manquants".

The possibility of the extinction was not largely accepted before the XIXe century.

When certain areas of the world were not yet completely explored and were not charted, the scientists could not eliminate the possibility that the animals only found in fossil form did not hide simply in unexplored zones of the sphere. One allots to Georges Cuvier the presentation of the extinction in fact in a lecture of 1796 with the Institut of France.

Implication of the man in the phenomenon

The phenomenon of extinction is an important field of research in Zoologie, and Biologie in general, and also became a subject of interest outside the scientific community. A certain number of organizations, like WWF, were created with an aim of preserving the species of the extinction. The governments tried, by enacting laws, to prevent that the man does not overexploit a species or does not destroy its habitat. Although several extinctions caused by the man were it by accident or negligence, certain deliberated combat were started with an aim of éradiquer certain species, like dangerous viruses.

The biologist Bruce Walsh of the Université of Arizona notes three reasons of the scientific interest for the safeguarding of the species: genetic resources, the stability of the ecosystems and the ethical ,

At the time modern, the commercial and industrial interests often enter in conflict with the interests conservationnists. When commercial technologies are tested, the test tends to concentrate only on its effects on the man. Nevertheless, of technologies having a null or tiny impact on the man can appear seriously harmful for the wild life (for example DDT). In extreme cases, these new processes can themselves cause involuntary extinctions like side effect. The biogéographe Jared Diamond notices that although the large companies denounce a certain exaggeration around the threats of extinction, some find their interest to adopt a policy of communication around good practices of nature conservation which they can set up, sometimes exceeding the committed efforts by organizations dedicated to the nature conservation like the national parks.

The governments see sometimes the loss of local species like a loss for the ecotourism and can enact laws envisaging a severe punishment against the trade of the species autochtones, in order to prevent the extinction in nature. natural reserves are created by the governments like a means of providing in a durable way of the natural habitats to the species oppressed by the human expansion. The Convention on biological diversity of 1992 allowed the installation of action plans for the biodiversity trying to provide comprehensible guiding lines for the projects of conservation of the biodiversity of the governments. Groups of support like the " Wildlands Project" and l'" Alliance for Zero Extinctions" , work to educate the public and to make pressure on the governments so that they take initiatives of conservation.

People who live close to nature can be dependant on the survival of all the species of their environment and could be regarded as those which are concerned with the risks of extinction. However, because of human overpopulation in the tropical poor countries, of enormous pressures are exerted on the forests by the Agriculture of subsistence and the imprudent use of the agricultural techniques of Brûlis. Consequently, the indigenous populations from day to day support survival with the conservation of the species.

Planned extinction

The man sometimes ardently worked with éradiquer several species of virus in an objective of fight against the diseases. For example, the virus of the Variole from now on is regarded as extinct in nature - although samples are preserved in certain laboratories, and the virus of the polio is now confined with some reduced areas of the sphere thanks to the efforts of the man to cure the disease which it causes.

Olivia Judson is one of some modern scientists to argue in favor of the extinction deliberated on certain species. Its article " In Bug' S Death" September 25th 2003 in the NewYork Times, defends the cause of the " specicide " of thirty species of Mosquito S thanks to the introduction of a gene " knock out" Recessive. Its arguments to act thus are that the mosquitos anophèles (vectors of the Malaria) and the mosquitos aèdes (vectors of the Dengue, the Yellow fever, the elephantiasis and other diseases) represent only 30 species; the éradiquer could save at least a million human lives at the price of a reduction of the genetic Diversité of the Culicidae from only 1%. Olivia Judson is even further arguing than since the extinctions of species occur all the time, the disappearance of some species moreover is not likely to destroy the ecosystem: We' Re not left with has wasteland every time has species vanishes. Removing one species sometimes shifts causes in the populations off other species - different goal need not mean worse."
One is not found with a damaged ecosystem with each time a species disappears. To eliminate a species generates sometimes changes for other species, but it is not necessarily into worse. Moreover programs anti Malaria and of control of the populations of mosquitos offer only one realistic weak hope to the 300 million people in the developing countries which are infected each year; although tests are in hand, Olivia Judson written that if they fail: " We must consider the radical solution (i.e to exterminate the mosquitos).

Cloning of extinct species

The concept of Clonage of the extinct species was made famous in the novel and successful film Jurassic Park . Although no extinct species was still recreated, recent technological advances encouraged the assumption that thanks to the process of cloning, an extinct species could be " brought back to the vie".

The subjects of study of cloning include the Mammouth. The cloning of an extinct species was not tried yet, mainly because of technological limitations, in addition to the objections Bioéthique S and Philosophique S that such an attempt can raise. DNA is preserved badly, and it is not very probable that the DNA from organizations which lived 10.000 years ago cannot never be found .

A recent programme of cloning of a subspecies of Ibex of the Pyrenees, Capra pyrenaica ssp. pyrenaica , was engaged in 2003, in order to try the restoration of the subspecies, disappeared on January 6th, 2000 following death from the last individual, in the National park of Ordesa and of Mount-Lost in the Spanish Pyrenees. The first attempt in 2003 of cloning, starting from fabrics taken on the last female of the subspecies before its death, has nevertheless leads to a failure, the embryos obtained not having survived beyond the second month of gestation. The experiment constitutes nevertheless a first, encouraging according to the researcher as a chief responsible for the project, Jose Folch.

So that a programme of cloning of extinct species can succeed, a sufficient number individuals will have to be clones (in the case of organizations with sexuée Reproduction) in order to create a population of viable size and in order to avoid in particular the phenomena of genetic Dérive.

Conservation of the species threatened of extinction

See also: Contenu=Articles detailed: [[Nature conservation]], [[Conservation in-situ]] and [[Conservation ex-situ]], [[ex-situ]], [[Statute of conservation]]

The awakening by the man of the acceleration of the extinctions of species, in particular those due to the impact of its activities, supported the emergence of the movements of nature conservation throughout the world.

The means of actions to try to preserve the species threatened of extinction are multiple. First of all by the creation of organizations specifically dedicated to the nature conservation on various scales and in many parts of the world: modest associations of environmental protection room, with the governmental organizations and great world institutions of nature conservation (Greenpeace, UICN, Ocean Conservancy, International Birdlife, etc). A common nomenclature of the threats of extinction will then be worked out, leading to the creation of the Statut of conservation " extinct with the state sauvage". The species listed under this statute by the world Union for nature (UICN) do not have alive specimens known in wild nature and are maintained in artificial zoo S or other environments. Some of these species are functionally extinct because they do not form any more part of their natural habitat and it is very improbable only they can turn over to a wild life. When that is possible, the zoological institutions modern try to maintain a population viable to ensure the safeguarding of the species and a possible reintroduction in nature by means of programs of conservatory breeding.

The creation of protected areas, like the national parks, the natural reserves, the reserves of biosphere, etc is another paramount tool for the conservation of species threatened of extinction. Sometimes created explicitly for the protection of a species in critical danger of extinction, this tool can appear effective (like the National park of Vanoise in France, created for the protection of the ibex of the Alps Capra ibex which saw its stabilized manpower), or quite to the contrary did not allow to preserve the species threatened of its territory (like the National park of Ordesa in the Spanish Pyrenees, which could not preserve the subspecies Capra pyrenaica pyrenaica of the Bouquetin of the Pyrenees, whose last individual died in 2000).

Finally international treaties were drawn up in order to fight against the disappearance of species. For example the Convention on the international business of the species of fauna and flora savages threatened of extinction signed on March 3rd, 1973 with Washington (QUOTE according to the Anglo-Saxon initials, also known under the name of “Convention of Washington”) is an intergovernmental agreement from which the objective is to protect the Espèce S Animal are and Végétal are threatened of extinction by the international exchanges by controlling the trade.

List few disappeared species

As it is indicated in the chapter " Causes " , the extinction of a species is in general due to several factors. An good example is the case of the Étourneau of Bourbon, bird endemic of the island of the Meeting whose causes of extinction are numerous:
  • invasive species: introduction of rats on the island;
  • disease introduced into the island;
  • competition: in competition with the sad Martin;
  • natural disaster: multiplication of forest fires;
  • destruction of the habitat: deforestation

However, for certain species disappearance is due to a major phenomenon:

Disappeared animal species

See also: List of the disappeared animal species, List of the species of birds disappeared

Disappeared plant species

See also: List of the disappeared plant species

  • the Prêle S giants.

Mankind and pre human disappeared

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