Endangered frogs
Declining amphibians - a global perspective
Declines in amphibian populations have been documented world wide since 1989. Herpetologists at the First World Congress of Herpetology meeting in Canterbury, realised in discussions with colleagues, there was anecdotal evidence of frog declines occurring in a number of countries.
The difficulty which faces herpetologists is to determine if a frog population is declining or just undergoing normal fluctuations over seasons and years. In the last decade, since rigorous monitoring has been put in place, dramatic frog declines have been confirmed throughout the world. The global loss of many species over a short time including dramatic population crashes in undisturbed areas such as some national parks provided clear evidence that frogs are declining. It has been suggested as frogs are sensitive to environmental conditions, they may be likened to 'the canary in the coalmine', providing the first indications of a detrimental change in global environmental conditions.
Frog population declines
Several causes have been advanced for frog population declines. Some are obvious causes such as loss or modification of habitat. If swamps or other wetlands are drained or cleared frogs will have no place to breed, shelter and feed. Construction of man-made water impoundment may favour some frogs but may affect the less common stream or seepage frogs which do not breed in ponds. Other possible impacts are not so obvious and have been linked to world frog population declines. Disease, immunosuppression, ultraviolet radiation, climate change, weather patterns, environmental toxins or possibly a combination of these could be playing a significant role in frog declines. No general, single cause has been identified. Determining the cause of declines remains a complex and difficult problem especially where frogs in the habitat have had dramatic declines while others in that same habitat are surviving. Similar situations have occurred where upland, closed-forest stream frog populations have disappeared or declined, while lowland populations are persisting.
Potential causes
One of the most difficult problems is our lack of information on amphibian ecology, behaviour and distributions. Separating natural fluctuations from potential declines is necessary to determine causes. Experimental ecology will be essential in assessing potential causes and hopefully identifying the proximate cause in each decline Diseases in amphibians are poorly understood. Recent studies have documented many frog pathogens and diseases for the first time. Currently studies are progressing on a chytrid fungus which has been identified in the skin during the declines of Australian and Panamanian frogs. Increased UV-B has been postulated as a causal factor in declines of the western United States but in tropical areas of the world, including Queensland, there has been no evidence of increased UV-B levels.
Monitoring of frog populations is essential to understand population behaviour, but it will not identify the cause(s) of declines. However, it will assist in understanding 'normal' frog population needs and requirements and changes over time. Many members of the public are participating in this monitoring program and scientists world wide are working towards understanding and identifying causes of frog declines. In Australia, the Natural Heritage Trust is funding a number of programs addressing frog declines.
References
The following references will assist in obtaining more detailed information on amphibian declines.
Campbell, A. (Ed). 1999. Declines and Disappearances of Australian Frogs. Environment Australia: Department of Environment and Heritage, Canberra. Pp 234.
Tyler, M.J. 1997. The Action Plan for Australian Frogs. Wildlife Australia, Canberra.
Pechmann, J.H.K. and Wilbur, H.M. 1994. Putting declining amphibian populations in perspective: natural fluctuations and human impacts. Herpetologica 50(1): 65-84.
Alford, R.A. and Richards, S.J. 1999. Global Amphibian Declines: A problem in applied ecology. Annual Review of Ecology and Systematics 30: 133-165.
Web sites links
Amphibian disease
http://www.jcu.edu.au/school/phtm/PHTM/frogs/ampdis.htm
Action and Recovery Plans
http://www.biodiversity.environment.gov.au/index.htm
International Coordination
http://www.open.ac.uk/OU/Academic/Biology/J_Baker/JBtxt.htm
Last updated: 31 August 2005