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Frog Declines

Now Extinct - The Southern Day Frog © Hal Cogger
Now Extinct - The Southern Day Frog
© Hal Cogger

Introduction to Australian Frog Declines

With 216 frog species currently described and new species still being discovered, Australia is classed as a significant centre of amphibian diversity (Tyler 1997).

The fossil record inidicates that frogs have existed in Australia throughout a wide range of climatic changes and other environmental disturbances for approximtely 45 million years (Tyler 1997). Their persistance through major environmental changes over time makes the drastic decline in species that has occurred over recent years a cause for considerable concern.

According to the Global Amphibian Assessment 2004, approximately 165 of the world’s known amphibian species may already be extinct with another third classed as threatened (GAA 2004).

The need to understand the causes underlying these declines has been recognised by the scientific community and dedicated action to arrest the continued decline in species is now underway at various levels.

Click on the following links to find out more about:

The History of Australian Frog Declines
Causes of Frog Declines
Classification of Conservation Status
Australia's Extinct Frogs
Australia's Critically Endangered Frogs
Australia's Endangered Frogs
Australia's Vulnerable Frogs
Australia's Near Threatened Frogs
Further Information on Frog Declines
References


History of Australian Frog Declines

In the 1980’s it was discovered that two unique Australian species, the Southern Day Frog (Taudactylus diurnus ) and the Southern Gastric Brooding Frog (Rheobatrachus silus ) had disappeared from their entire range. The cause for their apparent extinction could not be identified.

At the same time across the world, similarreports of species loss were emerging. The global nature of the problem came to light during the First World Congress of Herpetology in 1989.

This realisation was to be the beginning of a new consolidated global effort to arrest the drastic decline of amphibians species worldwide. Since this time there has been significant action towards halting the global decline of ampibians. One of the most important factors in arresting this decline is understanding its causes.

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Causes of Frog Declines

The reasons behind the sudden decline in frog numbers over recent years are still being investigated. Scientists are finding out more every day about the how different activities can combine to impact on frog survival.

The effects of human activities upon frogs and frog habitats are well documented and include disruption and destruction to natural habitats, the introduction of non-native species, and the use of herbicides and pesticides.

While the reasons for many local losses of frogs can be put down to specific causes such as these, the decline and disapperance of frogs in Australia and other continents from relativelty undisturbed habitats indicates that direct human activities are not solely responsible for all declines. Indirect threats such as climate change, which are the summation of long-term human activities may also play a large part in combination with direct human impact to threaten frog populations.

Just as the emergence of new infectious diseases such as Avian Influenza are a threat to human and animal populations across the world, amphibian species are also facing their most significant threat from a little understood disease. A chytrid fungus understood to be of the major causes of frog mortality across the world. More information on chytrid can be found on the Diseases page.

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Classification of Conservation Status

The International Union for the Classification of Nature (IUCN) uses an extensive series of threat categories, primarily based on the level of extinction risk faced by the species in question. This risk is defined by a further series of criteria. The categories relevant to the Australian frog fauna have been summarised below. For a more detailed explanation of these criteria, go to http://www.iucnredlist.org/info/categories_criteria2001.html

Extinct: A taxon is Extinct when there is no reasonable doubt that the last individual has died. A taxon is presumed Extinct when exhaustive surveys in known and/or expected habitat, throughout its historic range have failed to record an individual.

Critically Endangered: A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future.

Endangered: A taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future.

Vulnerable: A taxon is Vulnerable when it is not Critically Endangered or Endangered but is facing a high risk of extinction in the wild in the medium term future.

Near Threatened (Lower Risk): A taxon is Near Threatened or Low Risk when it has been evaluated, does not satisfy the criteria for any of the threatened categories, but is close to qualifying in the near future.

Data Deficient: A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution are lacking.

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Australia's Extinct Frogs

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Australia's Critically Endangered Frogs

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Australia's Endangered Frogs

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Australia's Vulnerable Frogs

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Australia's Near Threatened Frogs

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For further information on frog declines visit:

Declining Amphibian Populations Task Force - About amphibian declines
http://www.open.ac.uk/daptf/declines/decl0.htm

James Cook University - Amphibian declines in Australia
http://www.jcu.edu.au/school/tbiol/zoology/herp/decline/decl.shtml

Australian Museum Collections - Australia's lost frogs
http://www.amonline.net.au/collections/herpetology/frogs.htm

Department of Environment and Heritage - Declining frogs in Australia
http://www.deh.gov.au/biodiversity/threatened/information/declining-frogs.html

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References

The Global Amphibian Assessment (GAA) - Assessment of the world's 5,743 known species of amphibians http://www.globalamphibians.org/index.html

Tyler, Michael J. (1997) The Action Plan for Australian Frogs. National Parks and Wildlife, Canberra.

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