Decline in amphibian populations
Although the scientists observed a decline in populations of several species in Europe since the 1950s awareness of declining amphibian populations may lead to extinctions mass species in the world dates only from the years 1980. In 1993 already more than 500 species of frogs and salamanders present on five continents showed a decline in population Today, the phenomenon of declining amphibian populations affects thousands of species in all types of ecosystems and is recognized as one of the most severe threats in terms of species extinct or endangered in the against the biodiversity of our planet
The golden toad (Bufo periglenes), was an early indicator of declining amphibian populations. Regarded in the 1980s as abundant in its habitat in Costa Rica, it has been observed for the last time in 1989 The latest figures of population growth consistent with the normal date of 1987. In 1988, only 8 males and 2 females were observed. In 1989, it has met more than one male specimen, which is still the last person seen.
The original reports on the decline were not taken into consideration by the entire scientific community. Some scientists put forward the fact that animal populations, such as those of amphibians, known natural fluctuations over time. Today, all agree that the phenomenon of decline is alarming proportions throughout the world and the is expected to persist much longer
These extinctions and drops in amphibian populations are a global problem, the causes varied and complex. These include local factors such as fragmentation and destruction of natural habitats and the introduction of new human predators in the ecosystems in question, overexploitation of amphibians (food, medicine ...), increasing the toxicity and the acidity of the media lives of amphibians, the emergence of new diseases, the climate change, increased ultraviolet radiation (a result of attacks on the layer of ozone) and the likely interactions between these factors.
With the growing number of endangered species, a strategy of conservation has been established at international level to combat the multiple causes of amphibian declines. The main control methods used are the protection of natural habitats, the captive breeding, reintroduction and the eradication of some invasive species.
The fact that most amphibians have a way of life both terrestrial and aquatic, and their skin is very permeable suggests they may be more vulnerable than other species of terrestrial vertebrates the toxins present in the environment, as well as changes in temperature of precipitation and of humidity. Scientists then began to consider the amphibian biodiversity as a leading indicator of reference, indicative of the pollution generated by human activities and the effects it might have on other animal species.
The amphibians are a group of vertebrate organisms, comprising approximately 6 000 known species, bringing the Anura (frogs, toads, toad, frog ...), the urodeles (newts and salamanders) and Gymnophiona (caecilians, or legless). The group of amphibians has been about 360 Ma, and has already been described in the single period 1970 - 2000, the probable extinction of about 168 species. In addition, at least 2 469 species known (43% of amphibians) have shown a decline of their populations, indicating that the number of endangered species likely continues to increase
An international convention of biologists gathered in 2004 indicated that 32% of amphibian species worldwide are in danger of extinction (which represents 1 856 species) and over 120 species are already extinct since 1980 .
The population declines have been particularly intense in the western United States in Central America and South America, and in the east of the Australia. Thus in 2006, 16 of 45 species of amphibians in Canada (36%) have declined so drastically that they are now considered endangered, threatened or of special concern However, most cases of isolated amphibian extinctions occur in various parts of the globe. Thus, the IUCN estimated in September 2006 that a quarter of Mediterranean amphibians are threatened with extinction While human activities now cause considerable losses of biodiversity at the global level, it appears that their effects are much more serious and intense on amphibians as other groups of species
Because amphibians generally have a life cycle composed of two phases, the first water (tadpole) and the second terrestrial (adult organism), they are naturally sensitive to environmental disturbances, both terrestrial and aquatic. In addition, they may be due to their bare skin very permeable, more vulnerable to toxins in the environment than other organisms like birds or mammals. Many scientists are also convinced that the phenomenon of amphibian declines announced the possibility in the near future, a much broader phenomenon of mass extinction of biodiversity, this time extending to other groups of people live animals and plants
The phenomenon of amphibian declines was first widely recognized in late 1980, when a meeting of herpetologists reported having spotted an overall decline in amphibian populations Among the species most affected was the golden toad (Bufo periglenes) living in the reserve of the cloud forest of Monteverde, which was previously classified as a species common site. The Golden toad was at that time the subject of numerous scientific investigations, until 1987, when its population began to decline and eventually disappear completely in 1989 Other species of Monteverde, like the frog Atelopus varius (literally in Spanish Rana harlequin, harlequin frog), have also disappeared at that time. These individuals are located within a nature reserve, their destruction could be linked to human activities in the region. He had to look for causes to a more global scale, which has caused great concern among scientists.