Tasmanian Frogs

Amphibians are composed of three diverse groups of species. Salamanders and newts comprise some 300 species which are widespread through Asia, the Americas and Europe, while the Gymnophiona are a little known group of some 150 species of legless burrowing or aquatic amphibians predominantly confined to the tropics of Africa, Asia and South America.

The Anurans, or frogs, comprising some 4000 known species, are the best known group and the only Order of amphibians found in Australia. Some 94% of all Australia's 200 or so species - and all Tasmanian species - are believed to have evolved on the ancient southern continent of Gondwana, of which Australia and South America were a part. It is therefore not surprising to find that Australia's frogs have their closest affinities with South American species.

Many species of frogs throughout the world are in decline. These animals are particularly sensitive to changes in their environment, possibly as a result of the high permeability of their skin. As such, they are important 'biological indicators' of the health, or otherwise, of the Earth's ecosystems.

Development

Most, not all, species of frog pass through a larval (tadpole) stage. The word 'tadpole' is derived from a medieval English word meaning 'toad head'. The duration of the larval stage varies from species to species. The banjo frog spends 12-15 months as a tadpole, while the common froglet has a larval life span of 6-10 weeks. It has been shown that, in some species at least, the growth rate of tadpoles is related to the population density within the pond and the available food supply. All other things being equal, tadpoles in high densities grow at a slower rate than those occurring in lower numbers.

Adult frogs are carnivorous, unlike tadpoles which are herbivorous. The major part of their diet consists of a variety of insects. Food location is by sight. Prey needs to be moving to stimulate the frog into capturing its prey. The long, sticky tongue is flicked forward, ensnaring the prey.

Vocalisations

An obvious characteristic of frogs is their calls. Indeed, frogs may have been the first animals to communicate by sound. Only the males call. In many species, the ear is tuned to only a narrow range of frequencies, enabling a frog of a particular species to hear only the calls of its own species or species with a call of similar frequency. Calls are made not only to attract females, but also to advertise their presence. Many frogs also emit a 'release call', used when a male grasps another male with the misguided intention of mating.

The call of each of the Tasmanian species is provided as a sound file on the individual species' page.

Chytrid Fungus

Chytrid (pronounced kit-rid) fungus (Batrachochytrium dendrobatidis) causes the disease known as chytridiomycosis or chytrid infection which currently threatens Tasmania's native amphibians. The fungus infects the skin of frogs destroying its structure and function, and can ultimately cause death. Sporadic deaths occur in some frog populations, and 100 per cent mortality occurs in other populations.

Chytrid infection has been devastating to frog species, causing extinctions worldwide. The international trade of frogs probably brought the fungus to Australia from Africa. The disease has now been recorded in four regions in Australia - the east coast, southwest Western Australia, Adelaide, and more recently Tasmania. In mainland Australia chytrid has been implicated in the decline of ​43 species, including seven presumed extinctions, representing nearly a fifth of the country's amphibian diversity.

Resources

Chytrid fungus webpage

Tasmanian Chytrid Management Plan webpage

 Report on Amphibian Chytrid Fungus in the TWWHA (PDF 170Kb)