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Declining frog populations


Photo: Courtesy of Damon Ramsey

Declining Frog Populations
In the last few decades in different parts of the world, including north-eastern Australia, certain frog species have experienced drastic declines in what had been though of as relatively pristine rainforest streams. Many different causes have been implicated (see research on frogs under the Humans section later in this book). A fungus has now been implicated, and identified as Batrachochytrium dendrobatidis. It has dermal and systemic effects on the infected frogs. The fungus may have actually already been naturally present in the frog populations, with some sort stress bringing it up to more threatening levels.

Script: Courtesy of Damon Ramsey BSc.(Zool) Biologist Guide

Conservation of Frogs
Diseases, parasites and disabilities of frogs in wild and captive populations

All animals are affected by parasites, and amphibians are certainly no exception. In fact, because they live in moist, humid conditions conducive to life in general, they may catch more than their share. Certainly, many parasites such as the platyhelminth flatworms, leeches and insects prefer or may only to be able live and/or breed in such conditions. More recently, polluted waters have meant amphibians have been more likely to get bacterial infections form water.

An example of an obvious parasite on local frogs is provided by the endemic Australian genus of Batrachomyia flies. It seems quite common in the Green Eyed Tree Frog Litoria genimaculata of Wet Tropics streams. The adult lays an egg under the skin. This then hatch into a larva that is relatively large compared to the frog host, thus resulting in a hideous looking lump on the back or shoulder. The larvae poke a breathing hole through the amphibian's skin. It eventually emerges, often killing the frog host in the process. From there, it pupates in the ground.
Text: Courtesy of  Naturalist Guide Damon Ramsey

Population crashes and extinctions in frogs
All around the world, particular frog species were either going extinct or experiencing drastic declines in numbers. Many of the species effected were in high altitude, relatively pristine streams. Many different causes were implicated. The effect of Ultraviolet radiation on tadpole eggs was considered as the declines were often at higher altitude. Various diseases were also suggested, including fungal and viral agents. The frogs were living in freshwater, which implicated water borne contagion. Moreover, they were high alititude, suggesting an ecological effect of an agent that may not be able to infect animals at higher (lower altitude), temperatures.

A fungus has also been implicated in some of the declining and disappearing frog populations around the world. The fungus has been identified as Batrachochytrium dendrobatidis and has dermal and systemic effects on the infected frogs. The fungus may have actually already been naturally present in the frog populations, with a particular stress may have bringing it up to such threatening levels. A cooperative study between James Cook University and NASA suggested there was a correlation between the time just before the population crashes, and certain climate extremes. There were also suggestions that the disease may have spread from captive specimens. The stress in the populations of these frogs may have been previous to the crashes and indicated by disabilities or abnormalities in individual frogs. By incredible scientific fortune, surveys of amphibians were actually being undertaken before, during, and after the `crash'. The surveys measured limbs of the caught frogs and found evidence of asymmetry. This is a technique often utilized in the analysis of insect ecology to detect population stress.

Of the amphibians, only the frogs are found in Australia. Frogs can be simply defined as tailless amphibians. They have two shorter front limbs and two very long hind limbs. This body plan facilitates jumping very effectively and this design has obviously been successful as it has changed little over million of years. Like other amphibians, frogs skins are relatively permeable; that is many liquids and gases can pass through into their body. Frogs thus require a moist environment for this reason and for reproduction, and are also thus sensitive to environmental conditions.
Text: Courtesy of  Naturalist Guide Damon Ramsey


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Lake Eacham, Atherton Tablelands
Tropical North Queensland, Australia.
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