Decline in amphibian populations
The possible causes include habitat destruction and modification, diseases, exploitation, pollution, pesticide use, introduced species, and ultraviolet-B radiation (UV-B).
In the past three decades, declines in populations of amphibians (the class of organisms that includes frogs, toads, salamanders, newts, and caecilians) have occurred worldwide.
Because these species were located in the pristine Monteverde Cloud Forest Reserve, and these extinctions could not be related to local human activities, they raised particular concern among biologists.
They argued that the lack of long-term data on amphibian populations made it difficult to determine whether the anecdotal declines reported by biologists were worth the (often limited) time and money of conservation efforts.
[citation needed] However, since this initial skepticism, biologists have come to a consensus that declines in amphibian populations are a real and severe threat to biodiversity.
While human activities are causing a loss of much of the world's biodiversity, amphibians appear to be suffering much greater effects than other classes of organism.
The causes of these declines are complex, but many can be attributed to emerging diseases, climate change, increased ultraviolet-B radiation, or long-distance transmission of chemical contaminants by wind.
[20] There is considerable evidence that parasitic trematode platyhelminths (a type of fluke) have contributed to developmental abnormalities and population declines of amphibians in some regions.
The early larval stages of the trematodes then are transmitted into aquatic tadpoles, where the metacercariae (larvae) encyst in developing limb buds.
A study showed that high levels of nutrients used in farming and ranching activities fuel parasite infections that have caused frog deformities in ponds and lakes across North America.
Experimental studies have also shown that exposure to commonly used herbicides such as glyphosate (Tradename Roundup) or insecticides such as malathion or carbaryl greatly increase mortality of tadpoles.
[26] Although sex reversal in some species of frogs occur naturally in pristine environments, certain estrogen-like pollutants can forcibly induce these changes.
[27] In a study conducted in a laboratory at Uppsala University in Sweden, more than 50% of frogs exposed to levels of estrogen-like pollutants existing in natural bodies of water in Europe and the United States became females.
[30] Like many other organisms, increasing ultraviolet-B (UVB) radiation due to stratospheric ozone depletion and other factors may harm the DNA of amphibians, particularly their eggs.
Salamanders and frogs that produce less photolyase, an enzyme that counteracts DNA damage from UVB, are more susceptible to the effects of loss of the ozone layer.
More than three dozen species of amphibians have been studied, with severe effects reported in more than 40 publications in peer-reviewed journals representing authors from North America, Europe and Australia.
Researchers included this subtle connection in their inclusive climate-linked epidemic hypothesis, which acknowledged climatic change as a key factor in amphibian extinctions both in Costa Rica and elsewhere.
Amphibian populations in the beginning stages of decline often exhibit a number of signs, which may potentially be used to identify at-risk segments in conservation efforts.
[citation needed] Learning to identify such signals in the critical period before population declines occur might greatly improve conservation efforts.
The ASG is a global volunteer network of dedicated experts who work to provide the scientific foundation for effective amphibian conservation action around the world.
The ACAP (Gascon et al 2007), concerned that time and capability were short, recommended that all relevant species be immediately incorporated into ex situ breeding programs.
Conservation efforts through the use of protected areas have shown to generally be a temporary solution to population decline and extinction because the amphibians become inbred.
