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Frogs consist of more than 5,000 species described and they are among the most diverse groups of vertebrates. However, populations of certain frog species are declining significantly. Of the thousands of species of frogs, here are the most bizarre and oddest-looking.
From the site of its introduction, Bd spreads through water courses and amphibian-to-amphibian contact, and possibly by other mechanisms not yet fully understood. In Central America, where the spread of Bd has been extensively studied, its rate of progression has been calculated at 28-100km/yr.
Where Bd thrives, generally moist cool habitats, 50% of amphibian species and 80% of individuals can be expected to disappear within 1 year (Lips et al. 2006; www.amphibianark.org/Lips%20et%20al%202006.pdf). Currently it cannot be stopped in the wild and a minority of species seem able to survive with a Bd infection as larvae or as adults and these animals likely serve as a reservoir and vectors for future outbreaks. Notable among resistant species are worldwide invasive pest species including marine toads, American bullfrogs and African clawed frogs.
The study showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance and reproduction of a snail species that hosts microscopic parasites known as trematodes, said Assistant Professor Pieter Johnson of CU-Boulder's ecology and evolutionary biology department.
Five years ago there was a study in Wyoming; 92 percent of the frogs had abnormalities in the contaminated areas. Five years later the study was and the same area was no longer contaminated with Atrazine. In addition, there were no chemically castrated frogs found. According to Hayes and his studies, these frogs are more likely to be found in areas with Atrazine exposure.
In California, this decline has spanned 15 to 20 years. Experts say they are not aware of a single frog population that has significantly increased during that time, while many have disappeared.
This species of African clawed frog is neither threatened nor endangered. Presumably as a result of pet release, they have been introduced into Orange and San Diego counties in California, Arlington, Virginia, and Delaware, where they are now pests, devouring native wildlife such as fish, frogs, tadpoles.
Remarkably, the team found that frogs collected in habitats with foliage coverage of 20% or less were physically 5 to 10% smaller than those collected in habitats with 70% or more foliage cover. They also found that the frogs collected in more disturbed habitats had bodies that were less symmetrical than those in pristine areas.
The sex hormones that control reproduction and development in humans control many of the same functions in frogs. The effects are most critical to both species during early development. For example, some tadpoles exposed to androgens never develop into adults. "If you saw them in the field," says Hayes, "they look like big healthy tadpoles, but they never develop into frogs. The hormone inhibits their thyroid gland so they're stuck in the tadpole stage."
That still is a factor, the researchers say, but it also appears to involve a synergistic effect with the actual depth of the water. Quite simply, deeper water shields the toad eggs from some of the damaging effects of UV-B radiation. The toads have evolved to always lay their eggs in the same location with relatively shallow water that, in the past, apparently provided the optimal combination of warmth for quick hatching and adequate protection from UV-B radiation. But when the water levels dropped too low at that location due to lower winter precipitation, the eggs were exposed to much higher levels of UV-B radiation, the scientists found. They then weakened and became vulnerable to the opportunistic fungus that ultimately killed them by the thousands.
Our experiments not only document the
impact of exogenous sounds on anuran amphibian
choruses, but also bring to light the possibility of a
human disturbance diﬀerentially aﬀecting members of a
Before the earthquake, nearly 3,000 frogs were identified in numerous surveys over three years of study at the site. After the earthquake a total of 274 frogs were found in almost two years. As well, previous to the earthquake, the site had tadpoles from November to April, afterwards tadpoles could be found year-round, but at numbers 100 times less than before. From this data, it is obvious the earthquake significantly depleted the population or caused a massive migration.
50%: of ~6,000 described amphibian species, are threatened with extinction. 32% known to be threatened + 23% data deficient but believed threatened; ~3,000 species are in trouble.
165: number of amphibian species believed to have already gone extinct, including 34 known to be extinct, 1 extinct in the wild but still survives in captivity, and 130 not found in recent years and possibly extinct.
500: estimated number of amphibian species whose threats currently cannot be mitigated quickly enough to stave off extinction, i.e., those who require ex situ intervention.
10: number (not percentage) of amphibian species North American zoos are currently prepared to manage long-term.
50: that same number extrapolated (extreme best-case scenario) to the global zoo community.
10%: portion of amphibian species threatened with extinction that the global zoo community is at best currently prepared to manage.
The Global Amphibian Assessment (GAA) revealed that almost a third of amphibians is threatened with extinction. In response to these alarming findings, a Summit was convened in Washington, DC in September 2005 to craft a response by the International community. The resultant Declaration outlined four interventions that would be necessary to stem the crisis. It was also recognized that an entity was required to coordinate the implementation of a more comprehensive Amphibian Conservation Action Plan (ACAP). The ASG was formed to take on this roll. The ASG is Co-Chaired by Claude Gascon and Jim Collins and consists of a Global Network of some 600 partners. The ASG is responsible for keeping the GAA current to prioritize and support projects around the world to protect critical amphibian habitats. Various funding schemes are also offered for conservation. ASG publications include the Amphibian Conservation Action Plan (ACAP) and a bimonthly newsletter, Froglog. The ASG is building on the ACAP by catalyzing National and Regional Action Plans to advance amphibian conservation. If you are interested in becoming a member of the ASG, please contact the appropriate Chair for the Region in which you work, or contact us with any questions
Chytridiomycosis is an infectious disease of amphibians, caused by the chytrid Batrachochytrium dendrobatidis, a non-hyphal zoosporic fungus. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South America, eastern Australia, and Dominica and Montserrat in the Caribbean. The fungus is capable of causing sporadic deaths in some amphibian populations and 100% mortality in others. There is no effective measure for control of the disease in wild populations. The disease is contributing to a worldwide decline in amphibian populations, a worldwide decline of species that apparently has affected 30% of the amphibian species of the world..
Chytridiomycosis is believed to adhere to the following course: zoospores first encounter amphibian skin and quickly give rise to sporangia, which produce new zoospores . The disease then progresses as these new zoospores reinfect the host. Morphological changes of amphibians infected with the fungus include a reddening of the ventral skin, convulsions with extension of hind limbs, accumulations of sloughed skin over the body, sloughing of the superficial epidermis of the feet and other areas, slight roughening of the surface with minute skin tags, and occasional small ulcers or hemorrhage. Behavioral changes can include lethargy, a failure to seek shelter, a failure to flee, a loss of righting reflex, and abnormal posture (i.e. sitting with the hind legs away from the body)