Sunday, May 4, 2014

Amphibian Decline

Frogs have existed on Earth for 300 million years, but 43% of all amphibian species are declining. Habitat loss, introduced predators, and environmental changes are some of the main reasons for their decline.




The Yosemite toad (Bufo canorus) is an endangered amphibian from the Sierra Nevada, California, USA. © 2004 Pierre Fidenci


The critically endangered Puerto Rican crested toad (Bufo lemur) occupies mostly rocky limestone outcrops of Puerto Rico and the Virgin Gorda Island. © 2006 Paddy Ryan


The critically endangered Chinhai salamander (Echinotriton chinhaiensis) lead a largely hidden terrestrial life. © 1999 Max Sparreboom


Rarely observed the critically endangered Baracoa dwarf frog (Eleutherodactylus orientalis) from Cuba is one of the smallest frog in the world. © 2004 Pierre Fidenci


Endangered amphibians worldwide

Amphibians have existed on earth for about 300 million years, yet within the last several decades more than 120 species are thought to have disappeared for ever because of human activities.

Amphibian populations have declined dramatically around the world since the 1950s even in virgin parts (e.g., national parks). This pervasive decline is the results of local, regional, and global human induced causes. In 2006, a total of 442, 738, and 631 amphibian species were classified as critically endangered (imminent risk of extinction), endangered (very high risk of extinction in the wild), and vulnerable (facing a high risk of extinction in the wild). Overall, 1 in 3 amphibians are at risk of extinction!

Local impacts
These impacts include habitat modification, amphibian collection, and non-native species introduction. Habitat modification can be divided into three types: habitat destruction, habitat fragmentation, and habitat degradation.

Regional impacts
These impacts include habitat modification, amphibian collection, and non-native species introduction. Habitat modification can be divided into three types: habitat destruction, habitat fragmentation, and habitat degradation.

Global impacts
These impacts include environmental estrogens, climate change, and diseases (e.g. fungus Batrachochytrium dendrobatidis).


Data from IUCN, Conservation International, and NatureServe. 2006. Global Amphibian Assessment

Endangered amphibian species are found near all over the planet (Table 2), however, some regions of the world have been more affected than others. The worst places include Haiti, montane southeastern Chiapas, Mexico through central Guatemala, montane Costa Rica and western Panama, the Andes of Colombia and Ecuador, and the central portion of the Atlantic Forest in eastern Brazil.

At the regional scale, amphibians in the Caribbean are most threatened (84% of the region’s 171 species) due to high habitat loss, followed by Mesoamerica (685 species) , South America (2,065 species), and North America (262 species). Countries with the highest number of threatened amphibians (more than 100 amphibians per country) include Colombia (209), Mexico (196), Ecuador (163), and Brazil (110).

Distribution of Threatened Amphibians in Central America, Northern South America, and the Caribbean

Data from IUCN, Conservation International, and NatureServe. 2006. Global Amphibian Assessment


Table 2. Examples of worldwide critically endangered amphibians

Data IUCN 2006



Here are nine of the most endangered species of amphibians. Eight of the species are still being studied or bred in the Center for Conservation and Research at Omaha's Henry Doorly Zoo & Aquarium. One success, the eastern hellbender, has been released to the wild, although some of them are on exhibit at the zoo.
The “at zoo” numbers are only for the Omaha zoo. The “in the wild” numbers are estimates from scientific counts.




Puerto Rican crested toad
Native to: Puerto Rico
Adult size: 3-4 inches
Number in wild: 300
Number at zoo: 48
Loss of habitat has brought it close to extinction; it is critically endangered. Zoo is breeding them and has sent 11,000 tadpoles to Puerto Rico, but only 1 percent will become toads.




Mississippi gopher frog
Native to: Mississippi
Adult size: 3 inches
Number in wild: 60-100
Number at zoo: 303
Loss of habitat is its enemy. It has only one breeding pond in Mississippi. Zoo is testing Vitamin A as a nutritional supplement.




Blue spotted salamander
Native to: Iowa and states east and north of Iowa
Adult size: 3½-5½ inches
Number at zoo: 12
Doing well in eastern states but not Iowa. Attempts by the zoo to breed the Iowa salamanders in captivity failed; the zoo is working with Iowa Department of Natural Resources.




Panamanian golden frog
Native to: Panama
Adult size: 2-3 inches
Number in wild: 0
Number at zoo: 53
IUCN lists it as critically endangered. Zoo is having success breeding in captivity and is about to send some of its crop to other zoos. Can't release into the wild in Panama at this time.




Kihansi spray toad
Native to: Tanzania
Adult size: 1-1½ inches
Number in wild: 0
Number at zoo: 141
Habitat in waterfall spray zones has dried up. The zoo has created artifical spray zones and Tanzania is duplicating those. So if the toads will breed in captivity, they can be released in Tanzania.




Utah Boreal toad
Native to: one colony found on plateau Utah
Adult size: 2-5 inches
Number in wild: unknown
Number at zoo: 23
The toad occupies 1 percent of its historic breeding places in Utah. The zoo has had some breeding success but chytrid fungus is its biggest danger.




Wyoming toad
Native to: Wyoming
Adult size: 2 inches
Number in wild: One small colony in protected area in Wyoming
Number at zoo: 23
The zoo has released nearly 3,000 tadpoles and toadlets in Wyoming (remember 1 percent survival rate). The chytrid fungus remains a threat to its survival.




Striped newt
Native to: Two genetic groups native to Florida and Georgia
Adult size: 2-4 inches
Number in wild: unknown
Number at zoo: 200 of one genetic group (eastern)
Zoo has successfully bred its newts; the original 12 created 500. Western genetic group is smaller, more vulnerable.




Eastern hellbender
Native to: Ohio
Adult size: 11½-20 inches
Number in wild: unknown
Number at zoo: 8
The salamander is successfully being bred in captivity and released into the wild. Chytrid fungus is a danger to it, along with siltation of habitat and chemical runoff in streams.

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