Scientists organize the approximately 5,000 different frog and toad species into twenty-five families.
The ninety North American species span nine families. Approximately eighty per cent of those species fit into one of three families: true frogs (Ranidae); tree frogs (Tree Frogs) and true toads (Bufonidae).
A first of its kind report, the June 2007, the GAA listed a total of 5,918 amphibian species in the world.
Frogs and toads lead the list with 88% or 5,211 different species. Of those, 1,590 or 30.5% were listed as either vulnerable, endangered or critically endangered.
Salamanders and newts account for the second largest number of amphibian species with 535 or approximately 9% of the total. Of those, 249 or 46.5% were listed as either vulnerable, endangered or critically endangered.
Caecilians round out the list with 172 or a bit over 2% of the total. Of those, 5 or 2.9% were listed as either vulnerable, endangered or critically endangered.
The list is far from complete with little or no data on amphibian species entered for some states such as the Democratic Republic of Congo. Forthcoming data from other states such as Indian, Indonesia and Malaysia is anticipated to add to and alter the aggregate results. Therefore, current statistics need to be read as a first take comparative examination of global amphibian population trends.
Various reasons are given for population declines, with habitat loss cited as the primary causal factor. Amphibian population levels are exacerbated by two inter-related geographical factors. First amphibians are tied to both a specific geographical location and a specific habitat. Close to 90% of the world's amphibians live in a forest habitat. Global deforestation trends in the past couple of decades has contributed to declining amphibian populations.
Currently ten native frog and toad species are listed as either endangered or threatened under the terms of the Endangered Species Act. Habitat encroachment accounts for most of the stress on native frog populations. The introduction of non-native species accounts for other stresses. The bullfrog, for example, a nonnative, agressive species, was introduced into many ponds and lakes, where its subsequently chased off the native species. The Cane Toad in the video, the world's largest toad, continues to encroach on native species habitat in where ever it is introduced.
Another stress on frog populations, an amphibian skin disease called chytridiomycosis, caused by a chytrid fungus called Batrachochytrium dendrobatidis, Bd for short, takes on a sense of urgency as world wide frog populations continue to plummet.
Bd thrives in higher elevation, cool, moist habitats. In the United States, its presence has been most problematic in the Mountainous West, where a handful of species, including the Mountain Yellow-legged Frog population, an endemic species of the Sierra Nevada Mountains, have been affected.
East Coast frog populations, generally found in lower elevation, higher temperature habitats, have not been hard hit. Elsewhere, Bd outbreaks have caused severe stress on frog populations in Australia and Central and South America.
Recently a few, small research studies have shown promise for treating the fungus.
Chytridiomycosis in an aquarium collection of frogs: diagnosis, treatment, and control., reported that a small sample of frogs with Bd were cured following a treatment with an anti-fungal, itraconazole.
A March 2009 research report called Elimination of the amphibian chytrid fungus Batrachochytrium dendrobatidis by Archey's frog Leiopelma archeyi, showed positive results when using a topical anti-biotic called chloramphenicol.
Another March 2009 research report called Skin microbes on frogs prevent morbidity and mortality caused by a lethal skin fungus showed that the introduction of an "antifungal bacterial species, Janthinobacterium lividum" reduced mortality in a sample of Mountain Yellow-legged frogs.
While the research does not provide solutions for maintaining frog populations in the wild, they provide help for saving affected frogs in captive breeding programs. Further research might then provide avenues for neutralizing Bd in the natural environment, allowing for the reintroduction of healthy frog populations from the breeding programs.
The phrase poison frogs, often refers to two different groups of frogs:
Dendrobatidae, new world, neotropical frogs, inhabit tropical forests of Central and South America. Small in size, the nickname name poison dart frog came from the fact that indigenous peoples were known to use their poison on blow gun darts for hunting.
In addition to their small size, many Mantella and Dendrobatidae species are colorful, a reminder to remind potential predators in their territory to stay away.
Partly because of their toxicity, they are active during the day, hunting insects, their food of choice.
In fact, recent research from the National Academy of Sciences, Convergent evolution of chemical defense in poison frogs and arthropod prey between Madagascar and the Neotropics found that the frogs' poisonous alkaloids result directly from their diet. They consume poisonous insects, often ants and millipedes, and the poison accumulates in their skin.
Because the poisonous alkaloids are not naturally occurring, many poison frog species are raised as pets. After a time, feeding captive bred poison frogs non-poisonous insects, creates non-poisonous, poison frogs.
Currently the IUCN lists one hundred and fifty seven Dendrobatidae species arranged according to eleven genera. Close to thirty are listed as either endangered or critically endangered. However, that number could be substantially higher due to the lack of data available on all of the species.
Seven of the sixteen Mantella species are listed as either endangered or critically endangered.
© 2001-2014 Patricia A. Michaels