Although the scientists observe a reduction in the populations of several species in Europe since the Années 1950, the awakening of the decline of the populations of Amphibians which can involve massive extinctions of species in the whole world dates only from the Années 1980. In 1993 already, more than 500 Species S of frogs and salamanders present on the five continents presented a decline of population. Today, the phenomenon of decline of the populations of Amphibians affects thousands of species in all the types of ecosystem S and is thus recognized like one of the most severe threats, in term of disappeared or threatened species, against the Biodiversité of our planet.

In the beginning, the reports/ratios on this decline were not taken into account by the totality of the scientific community. Certain scientists advanced the fact that the animal populations, such as for example those of the Amphibians, knew natural fluctuations during time. Today, all agree to say that this phenomenon of decline becomes extensive alarming everywhere in the world, and one expects that it persists still a long time.

These extinctions and falls of populations of Amphibians are a world problem, with the various and complex causes. Among them appear of the local factors like the fragmentation and the destruction of the natural habitats, as well as the introduction by the new man Prédateur S into the ecosystem S in question, the overexploitation of the Amphibians (food, medicine…), increase in the Toxicity and the acidity of the mediums of life of the Amphibians, the emergence of news Disease S, the Climate change, increase in the ultraviolet radiations (consequence of the attacks carried to the layer of Ozone) and interactions probable between these factors.

In front of the growing number of threatened species, a strategy of conservation was installation at the international level in order to fight the multiple causes of the decline of the Amphibians. The principal means of fight employed are the protection of the natural habitats, the conservatory breeding, the reintroduction and the eradication of some invasive species.

The fact that the majority of the Amphibians have an at the same time terrestrial and watery lifestyle, and that their skin is very permeable leaves think that they could be more vulnerable than the other species the vertebrate terrestrial ones to the Toxine S present in the Environnement, like of the modifications of Température, precipitations and Hygrométrie. The scientists thus start to regard the biodiversity amphibienne as a precursory indicator of reference, revealing of the Pollution generated by the human activities and of the effects which it could have on the other animal species.

Context of the problem

The Amphibians form a gathering group of vertebrate organizations approximately: 6000 known species, gathering the Tailless (Frog, Clamping plate, Bell ringer, tree frog…), the Urodele S (salamanders and tritons) as well as the gymnophiones (apodal or cécilies). The group of the Amphibians exists since approximately 360 My, and it was already described, during the only time 1970 - 2000, the probable extinction of approximately 168 species. Moreover, at least: 2469 known species (43% of the Amphibians) present a decline proven their populations, which indicates that the number of species threatened of extinction probably continues to increase. However, of the cases more isolated from massive extinctions of Amphibians occur in various places of the sphere. Thus, IUCN estimated in September 2006 that a quarter of the Mediterranean Amphibians are threatened of extinction. Whereas the human activities cause now considerable losses of biodiversity on a world level, it appears that their consequences are definitely more serious and intense on the Amphibians that on other groups of species.

Since the Amphibians generally have a life cycle made up of two phases, the first watery one (Têtard) and the second terrestrial one (adult organization), they are naturally sensitive to environmental disordered states as well terrestrial as watery. Moreover, they can be, because of their naked skin very permeable, more vulnerable to toxins present in the environment than of other organizations like the Oiseau X or the Mammifère S. Of many scientists are convinced besides that the phenomenon of decline of the Amphibians announces to the possibility, in a near future, of a phenomenon much broader of massive extinction of the biodiversity, extending this time to the other groups from living beings, animals and plants.

The phenomenon of decline of the Amphibians for the first time was largely recognized at the end of 1980, when an assembly of herpetologists paid to have located a total regression of the populations of Amphibians. Other species of Monteverde, like frog Atelopus varius (literally in Spanish Rana harlequin , Frog harlequin), also disappeared at that time. These individuals being localized inside a natural reserve, their destruction could not be related to the human activities of the area. It was necessary to seek the causes on a more total scale of them, which generated great concern in the scientists concerned.

Natural fluctuations or problematic decline?

See also: Extinction of Holocene the

Years 1950 at the end of the Years 1980, certain researchers noticed a decline of the populations of Amphibians. This decline was, according to them a precursory index of the degradation of the natural environments. The scientific community showed skeptic on this criterion and the importance of this decline of the populations of Amphibians on a world level and the serious threat that constitutes for the biodiversity.

Potential causes of the decline

While being based on the searchs for James P. Collins and Andrew T. Storfer, two whole of assumptions on the decline was erected scaffolding.

The first includes the general factors concerning the crisis of the planetary biodiversity: destruction, modification and fragmentation of the natural habitats, introduction of invasive species and overexploitation of the resources. The study of these threats allows a better comprehension of the decline of the Amphibians, in its related aspects with the total ecological mechanisms. However, the decline touches also populations of Amphibians in environments moved back without apparent disturbances.

The second calls some with more complex factors and more élusifs, and is probably consisted the climate change, the increase in radiations UV-B, the rejection of chemical pollutants in the environment, of new emergent infectious diseases, as well as the deformations or malformations of the organizations. The mechanisms subjacent with these last factors are complex and can be added with the first factors, thus the destruction of the habitats and the introduction of introduced foreign species exacerbates the phenomenon of decline.

There is not only one cause isolated with the decline from the Amphibians. All the aforesaid factors threaten these populations with more or less high degrees. The majority of the causes of this decline are finally goods included/understood and explained. Beyond the Amphibians, other groups of organizations suffer from the same disturbances.

Destruction and fragmentation of the natural habitats

See also: Fragmentation of the habitats, Roadkill

The modification or the destruction of the natural habitats is the factor which, to the planetary scales, assigns more the populations of Amphibians. As the Amphibians generally require for habitats as well terrestrial as watery to survive, a threat weighing on only one of the two habitats can have serious consequences on their populations. The Amphibians are thus more vulnerable to the modification of natural environments than the organizations requiring one type of habitat.

The Fragmentation of the natural habitats occurs when the various zones favourable with the life of the Amphibians are isolated from/to each other by modifications in physical matter, as for example when a wooded surface is surrounded by all shares by zones of agricultural cultures. The small populations which remain in these remanent fragments often run a great risk of Endogamie, of genetic Dérive even of extinction due to weak fluctuations of the environment.

In the majority of the European countries, the disappearance of the wetlands relates to very important surfaces. Thus in Suisse these mediums have been reduced of almost 90% for 150 years, even of 100% in certain sectors. From 1953 to 1959, nearly 66% of the habitats of reproduction of the Alpine Triton, of the punctuated Triton, the Bell ringer to yellow belly, of the common Clamping plate, the green Tree frog, the green Frog and the russet-red Grenouille was destroyed in the upper part of the valley of the the Rhine in consequence of embankments and constructions of roads.

Since the years 1950, much of Amphibians of the Mediterranean region become very rare because of the destruction of their habitats.

The destruction of the wetlands constitutes the leading cause of the rarefaction of russet-red frog (more than 99% of extinction in certain sectors) and of the common clamping plate during the years 1950 and 1960 in Great Britain.

Certain species not living on their specific places of reproduction must migrate to reach the wetlands. The reproductive individuals expose themselves then, to pass to the outward journey and the return in zones where their safety is not assured. It is the case for the crossed road. When the places of laying are not accessible any more, a low wall can sometimes be enough so that the population disappears.

Introduction of immigrant species

See also: biological Invasion

The predatory and concurrent species foreign with the ecosystems affect the viability of the Amphibians in their own natural habitats. One detected a decline of population at Rana muscosa , species common of the lakes of the Sierra Nevada, with the the United States, had with the introduction of fish species, in particular of the Truite S raised for the sporting or entertaining Pêche. A great number of young individuals and Têtard S are the prey of these fish. These fish cause an interference in the triennial cycle of metamorphosis of the tadpoles and cause finally a severe decline of the population and, by rebound, touch the whole of the ecosystem. This phenomenon is far from being single, the introduction of the Lepomis gibbosus in North America contributed to reduce the populations of Rana will aurora and of Pseudacris regilla .

The introduction of Gambusia to fight against the mosquitos, of the Rainbow trout and the Truite fario for fishing is concomitant with the significant drops of manpower of the Litoria spenceri in Australian south-east. The zones of introductions corresponding to the zones of fall do not leave any doubt about the role of the introduced species. Gambusia affinis , introduced to fight against the mosquitos, seems to be in this case. -->

The introduction of the Ouaouaron, a large American frog, in various place of the world like Europe, the Antilles, South America, is also a threat for the other Amphibians. Indeed, the ouaouaron directly consumes specimens of other species smaller than and is to him an effective competitor for the others.

Exploitation of the Amphibians

The Amphibians are captured, moved out of their natural habitats and are sold in the whole world like food, pets, or to supply the pharmacological market. For several species, harvest is supposed Co-person in charge of their decline. In France, the legal frog importation is primarily for food reasons, in comparison the alive imports of the Anoura for the breeding or science is negligible. The harvest of certain species like pets, because of their protection because rarefying in their natural environments, is very often illegal and generates lucrative traffics.

Amphibians on the food market

The Anoures and more particularly their thighs are consumed by the Man, even if the edible frogs do not represent more than one about fifty species. The majority are indeed toxic and some have properties Hallucinogène S. the thighs of frog are extremely popular in Europe, with the Canada and the the United States. In 1990, Europe imported close to: 6000 tons of frog thighs coming from Asia. According to their ministry for agriculture, the French consumed: 3500 tons of thighs in 1994 is: 8000 tons or approximately 30 million frogs whose majority comes from imports. Between 1981 and 1984, the United States imported more: 3000 tons of frog per annum is approximately 26 million frogs.

Asia is the second major Marché food of Amphibians in the world, where the most consumed species is Hoplobatrachus rugulosus . According to the French customs statistics, on: 6400 tons of thighs imported in 2002: 3300 would come from wild species of Indonesia.

Amphibians like new pets (NAC)

For a long time, the children will collect tadpoles in the neighbouring ponds and ponds to raise them on their premises and observe the process of metamorphosis during which they become adult. However, the breeding of the Amphibians as NAC was popularized these last years, and it does not act from now on only children any more. Many Amphibians are sold in the animalist stores; and some pay very expensive for frogs with the bright colors and brilliant of which good number of specimen are taken directly in nature. In 2007,16 species are registered on appendix I and 90 on appendix II of the QUOTE. Not registered on this date, the Conraua Goliath , the largest frog of the world, which does not meet, in a natural state, which in some rivers isolated with the Cameroun and in Guinea Equatoriale, in Western Africa, is concerned with overexploitation. However principal the danger related to the NAC detention is the diffusion of diseases to the local species during release of exotic species.

The use of the Amphibians at educational and scientific ends

Many national education systems envisage in their school programs of biology of handling of Dissection of the Anoura. The great availability of frogs in fact of the ideal candidates for these dissections and in addition one waits until their cost is weak. The species most commonly used for this purpose are Rana pipiens (Frog leopard) and Rana catesbeiana (Frog-bull or Ouaouaron) but also in a frequent way for the laboratories of faculties of biology, the salamander Necturus maculosus (mottled Necture). Thus in 1976, harvests of Rana pipiens with the Manitoba for this purpose completely ceased because this one had practically disappeared from the province whereas it sheltered the strongest densities before of them. In addition to those taken in nature, of the breedings were launched in the Années 1980 to satisfy the request in the United States, but quickly delocalized with the Brésil and Taiwan for reason of profitability. These pollutants have variable effects on frogs: some reach and deteriorate the central Nervous system, whereas others, like the Atrazine, a Herbicide, cause a stop of the production process and of secretion of the hormones thus involving the sterility of the adults. Experimental studies showed that the exposure to others Herbicide S like the Roundup or to some Insecticide S like the Malathion or the Carbaryl causes a clear rise of mortality at the tadpoles. Additional studies indicate that the Amphibians developing in terrestrial environment are also vulnerable to Roundup and more particularly to the one of its components, the POEA (Polyoxyéthylèneamine) which is an agent Tensioactif, dampener (supporting the dispersion of the droplets on the treated plants) and not a Pesticide.

Years 1950 at the years 1970, the populations of Amphibians of the Mediterranean region, already very touched by the destruction of habitats, can be strongly affected by the excessive use of insecticides. After the insecticide spreading in the marshes of Aygade by the municipality of Hyères: 5,000 southernmost tree frogs were found died on March 8th, 1958. This pulverization of the French tourist localities of the Riviera practically eliminated the local populations from webbed Triton, Triton marbled and mottled Salamandre.

In the Hungarian plain, the common clamping plate became a rare species in the years 1960, its populations having suffered from a recourse growing to the weedkillers. In England, of 1965 to 1970, the frog populations were reduced dramatically in the counties of Essex, Surrey and Kent mainly because of pulverization to the DDT of the ponds and ditches. In this country, the decline of russet-red frog is also allotted to the use of a weedkiller.

According to a publication of approximately 1999,20% of the basins of the states and provinces bordering the Big lakes presented contents nitrates higher than those which can cause anomalies of the development and other effects sublétaux in the Amphibians, and 3% a sufficient content nitrates to kill them.

Pollution can also modify the acidity of the environment and especially of water. The acid rains, or acid snows in north, often do not threaten directly the Amphibians which are able to survive in passably acid water (pH 4), but they kill some Insecte S which constitute their preys.

The effect of chemical pollution can be differed: the death of adults can indeed occur only during the season of reproduction because of mobilization of liposoluble poisons stored the preceding summer by consuming contaminated food.

Emergent parasites and diseases

Many pathologies are recognized like factors responsible for the decline of the populations for Amphibians or at least persons in charge of massive deaths individuals. Among them, let us quote the disease known as “of the red members” (literal translation of English: red-leg disease ) (caused by the bacterium Aeromonas hydrophila ), necroses it hematopoietic epizootic (group of the Iridoviridae ) (caused by the Ranavirus as well as other diseases badly known like the Anuraperkinsus and the Chytridiomycose

; Trematodes

See also: Trematodes

Parasitic called Trématode S (junction of the Plathelminthes) intervene in the development of anomalies in the Amphibians, and thus in their decline. These Trematodes, of the kind Ribeiroia , have a complex life cycle since they affect successively three types of species-hosts. The trematodes first of all affect certain watery species of pulmonés gastropods (Escargot S). Then, arrived at the larval stage, they are transmitted to the tadpoles where the métacercaire S (larvae) enkystées penetrate inside the buds of members, which generates post-metamorphic anomalies in adult frogs, namely the absence of members or on the contrary the presence of additional members. One knows today that the majority of the extinctions of the species of these areas are related to this mushroom, which belongs to a family of micro-organisms Saprophyte S known under the name of Chytrides ( Chytridiomycota ) and who, in general, do not have pathogenic properties.

This disease generated by Batrachochytrium dendrobatidis is called Chytridiomycose. The infected frogs present central nervous system disorders, and in the long term the death of the animal. Experimental studies showed that the time passed between the infection and death was from to one or two weeks.

Subsequent research showed that the mushroom is present in Australia since the middle of the years 1970 and in North America since 1974 on Rana pipiens . It is present in Spain since the end of the year 1990.

One of the stocks was located for the first time at Rana muscosa , in the National park Kings Canyon in California. One thinks that it is responsible for massive deaths of Rana muscosa in 1979, just as of those of the Bufo boreas (Clamping plate of the west or boreal).

; Necroses hematopoietic epizootic

See also: Iridoviridae

Necroses hematopoietic epizootic is a viral infection caused by a Iridoviridae , a Virus with DNA. It is thought that some of them are responsible or Co-persons in charge of death rates extremely high and localized for Amphibians such as for example on a species of salamander in 1995-1996, placing it in danger of extinction. In 1997 and 1998, viruses of this family caused the death of striped salamanders and Rana sylvatica in Saskatchewan and of striped salamanders to the Manitoba.

The comprehension of the mechanisms inherent in the assumptions of climate change has a major complexity. The climate change can affect an area directly or to generate a series of successive events and to have thus an indirect effect on an area far away from the hearth of the climatic anomalies. Thus the assumptions of climate change are they intrinsically complex because they can assign the individuals and the populations directly, or indirectly while taking in this case sometimes years even of the decades before appearing. Among the effects of global warming, we can quote, for example, the growth or the premature reproduction of the individuals of certain species of Amphibians living in moderated climates, which are found thus confronted with an hostile environment (absence of food,…), characteristic of colder seasons during which they are supposed to hibernate.

A series of studies undertaken in tropical environments proved the existence of a relation of cause and effect between climatic irregularities and declines populationnels. With the Brazil, one described the extinction of 5 species of clamping plates, consequence of a series of frosts. One also detected, always in Brazil, that the declines of the populations of Amphibians could be connected to drier winters. In Porto-Rico, one also proved connections existing between the dramatic decline of the population of Eleutherodactylus coqui (in Spanish Coquí ) and the growing number of long periods of Sécheresse (characterized by a level of precipitations lower than 3 mm). Same manner, one clearly could connect the extinction of the Bufo periglenes ( , gilded Crapaud) of Monteverde, and the decline of other species of Amphibians of the area, with the frequential irregularities of the index of Hygrométrie of the ambient Brouillard of the tropical forests of Monteverde.

Other studies showed the reduction, during the periods of great dryness, the depth of the Mare S in which certain species of Amphibians deposit their eggs. This reduction of depth of water generates more strong exposure of embryos to rays UV-B, which increases the vulnerability with the diseases as that due to the mushroom Saprolegnia ferax which causes the death of eggs. Their genetic inheritance is then faded and their defective immune system. In certain ponds where the level of water is too low, the mortality of the embryos reaches 100%. The reduction in the immunizing responses in the Amphibians also involves a greater sensitivity to the attacks of parasites like the worm nematode Ribeiroia ondatrae , of mushrooms (of which Batrachochytrium dendrobatadis identified in 1998 and causing lesions of the skin) or of virus of the type Ranavirus .

Radiations UV-B

The levels of Radiation UV-B in the atmosphere increased significantly during the last decades. The researchers showed that radiations UV-B can kill the Amphibians directly, while acting jointly with pollution, the disease-causing agents and the climate change, on their premises to cause side effects like retardements of growth or dysfunctions immunizing, involving their death and thus their decline.

There exist three types of ultraviolet radiations: the GRAPE ones (of wavelength ranging between 315 and 400 Nm); UV-B (between 280 and 315 Nm) and UV-C (between 200 and 280 Nm). The majority of the Biomolécule S do not absorb radiations wavelengths equivalent to those of the GRAPE one, and most of radiation UV-C is absorbed by the stratospheric ozone (layer of ozone). Remain only radiations UV-B, which, with strong amount, have particularly harmful effects on the living organisms.

Radiation UV-B, following the Climate warming and with the thinning of the stratospheric Layer of ozone, increased significantly. The Amphibians are extremely vulnerable to radiation UV-B owing to the fact that their eggs are deprived of protective shell and that their skin, at the adult specimens as at the tadpoles, is fine and delicate. It is highly probable that this increase in radiation UV-B contributes significantly to the decline of the Amphibians.

The research undertaken on more than 10 species of Amphibians showed that a Enzyme, the Photolyase, was able to repair the damage caused with DNA by radiations UV-B. Experiments made in laboratory on eggs of the salamander Ambystoma gracile proved their vulnerability with radiations UV-B. It is probable that the species of Amphibians having an important enzymatic activity (of photolyase type) can repair the damage caused with the DNA by the exposure to the UV-B of manner more effective than of other species having a weak enzymatic activity of this type.

Deformities and malformations

One has noted for a few years an increase in the observations of deformities or malformations in the natural populations of Amphibians; this phenomenon was recently classified among more the environmental big problems.

During the summer 1995, a report drawn up by a professor of a school of Sweat, Minnesota, in connection with the rare deformations at Rana pipiens ( , Frog leopard), led to the opening of an investigation by the Agency of control of the pollution of Minnesota, which showed that 30% to 40% frogs present on the place of the observations had malformations. Thereafter, the biologists understood that these anomalies were not circumscribed in Minnesota, and that one described this kind of malformations (frogs and tritons with more than four legs or only two) in Amphibians of the whole world (nearly 80% in the most touched sectors).

There already was large Débat S on the malformations which have occurred in the Amphibians in their natural environment during which one realized that it was difficult to determine the causes of them. It is relatively easy to cause malformations on embryos raised in laboratories, but those always do not correspond to those which are observed in nature. In addition, it is not really known if the rate of malformations observed in the Amphibians really increased during the last years, or if the increase in the number of observations is due quite simply to the more paid great attention on this subject.

In spite of these uncertainties, malformations are seen like the result of multiple causes, which do not bind all to the damage caused with the environment by the human activities. The principal assumption charges the increase in the number of malformations in the Amphibians to an increase in the radiation levels Ultraviolet your (UV), rate of chemical Pollution and Parasitose S.

Strategies of conservation

The Global Amphibian Assessment created an action plan for the conservation of the Amphibians. This plan is articulated around four objectives with very short term: improvement of the comprehension of the causes of the declines populationnels and the extinctions; the diffusion of information on the biological diversity of the Amphibians and the changes which she knows; the development and implementation of programmes of conservation on the long run; the contribution of emergency answers to the current crises.

Here some of the means being able to reverse, attenuate or prevent the decline of the populations of Amphibians:

• Protection of the natural habitats : The loss and the degradation of the natural habitats affect 90% of the species of Amphibians threatened. The majority of them need conservation measures of their habitat to ensure itself to be able to survive. Consequently, the safeguard of habitat-keys where the threatened Amphibians can live and to reproduce in safety is the most urgent priority for the survival of much of species. Several types of measurements are often taken as for example:
• Responsabilisation of the farmers with payment of premiums for maintains wetlands and for the stop of the use of pesticides and weedkillers. To remove human installations like the plantations of tree along the wetlands and restoration of the banks.

• Breeding in captivity : Programs of breeding in captivity of certain threatened species are set up in this moment in the zoological gardens. The species thus raised could be reintroduced later on in their natural environment even if it poses today an important problem of reproducibility in the breedings after several years without it being included/understood why, that it is vital to be able to take immediate measures.

The organization of protection

It is the Global Amphibian Assessment , an organization resulting from the IUCN, which tried to draw up an assessment with the beginning of the year 2000, concerning the causes of disappearance. This will led to a study. This organization is a partnership between the Worldwide association of the zoos and the aquariums member of the IUCN and several sections for the conservation of the species of the UICN of which that of the Amphibians. The goal of Ark is to help its partners for a conservation '' ex-situ '' and to protect the natural sites. Another of its attributions is to really identify the Taxon S in danger since there exists an uncertainty of threat on nearly 23% of the species.

• Amphibian Decline: The Conservation Status off United States Specie , University off California Near, 2005, ISBN-10: 0520235924.
• Amphibians in Declines: Canadian Studies off has Global Problem , Society for the Study off Amphibians and Reptiles, 1997 ISBN-10: 0916984400.
• Amphibian Declines: Year Integrated Analysis off Multiple Stressor Effects , SETAC Near, 2003, ISBN-10: 1880611554
• Jean Rostan, life of the clamping plates . Paris, Stock, 1933,221 p.

Sources

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