This is one of my favorite websites. Generally when you think of frogs, you may think of a bullfrog, a poison dart frog, or Kermit. But most people
aren't aware of the vast diversity of Order Anura, or frogs and toads.
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.
Weird Frogs
So, the author of this site mentioned hat there is a decline in frog species. While you enjoy those awesome frogs, let's try and figure out what is
wrong with the frog populations all over the world. Frogs, like all amphibians, respire through lungs and skin. Their eggs are also shell-less. This
means that they are especially vulnerable to changes in their environment because in many ways, the conditions of the external environment become
conditions inside these organisms. Here are some possible explanations. The truth is that right now, scientists just don't know what the problem is.
They're attempting to treat each one of the causes, such as isolating and disinfecting frogs infected with Chytrid or removing frogs from areas with
parasites.
Chytrid Fungus (Bd):
www.amphibianark.org...
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.
Pollution and parasites:
www.sciencedaily.com...
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.
Pesticides and parasites:
media.www.ramcigar.com...
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.
www.npr.org...
www.recordnet.com.../20070608/A_NEWS/706080327/-1/A_NEWS
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.
Invasive Species:
Not only do invasive frogs and toads compete with native frogs and toads for food, but they also are carnivorous and eat the native species.
sofia.usgs.gov...
nationalzoo.si.edu...
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.
Deforestation:
If it's making frogs smaller, is it making some species disappear altogether?
www.newscientist.com...
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.
Birth Control Pills and Hormones in Water:
www.exploratorium.edu...
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."
Climate Change:
If it's killing toads, is it killing frogs, too?
www.anapsid.org...
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.
Increased Noise:
www.physci.ucla.edu...
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
multi-species community.
Earthquakes:
news.mongabay.com...
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.
Some Statistics:
www.amphibianark.org...
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.
My guess is that it's a combination of all the factors, and Chytrid and deforestation are mainly responsible in remote areas, and that pollution is
responsible in more urban areas, and invasive species are responsible everywhere. But regardless of the cause, these amphibians are decreasing and
decreasing quickly. We do not even understand nor have identified many species of frogs, and just as we are learning more about them and how they can
help us as bioindicators and in fields of research, they are disappearing. Enjoy the awesome frogs while they last, because in ten years many of these
species may be extinct.
For more information and for those who are interested, I'd like to direct you to PBS' series "The Thin Green Line" available here:
www.pbs.org...
[edit on 5/24/2009 by ravenshadow13]
