Michael J. Tyler
with the assistance of the Editorial Advisory Committee
Wildlife Australia, April 1997
ISBN ISBN 0 642 21400 X
There are approximately 4000 frog species in the world. The major centres of diversity are South America and Africa, whilst Australia and New Guinea are significant. Currently 208 named Australian species are recognised (see Appendix 1), although it is estimated that some 20-35 more await description or discovery. A new genus (and new species) from Tasmania has recently been described (Rounsevell et al. 1994) and another new genus (and species) description from Western Australia is awaiting publication (Roberts et al. in press).
The fossil record of frogs extends to the early Jurassic of South America. The earliest material from Australia is of the Eocene, from Queensland. The overall morphological conservatism of frogs over such an extensive period indicates that several extant genera have survived a wide range of climatic and other environmental changes over at least 45 million years. The dramatic and unexplained decline of many species in recent years is, therefore, a matter of severe concern.
Historically the study of frogs in Australia has attracted fewer contributors than any other Class of vertebrate. This assertion can be demonstrated in two ways: firstly by the fact that a review by Moore (1961) recognised only 92 species (less than 50% of the current total), and secondly by the fact that there is a very limited number of population studies against which population change can be quantified.
The habitats of frogs are even less well known. In the past 200 years the Australian landscape has been altered by urbanisation, land clearing, and water diversion and pollution on a large scale, especially in the south east of the continent. The effect of these activities on the conservation of the fauna, particularly the habitats available to species of frogs, has largely gone unnoticed.
The first evidence that Australian frog populations were in decline was provided by the disappearance of two species throughout their known range. The Mt Glorious Torrent Frog Taudactylus diurnus, only described in 1966, was last sighted in 1979 (Czechura and Ingram 1990). The Gastric Brooding Frog or Platypus Frog, Rheobatrachus silus, which was unknown until 1973, was last sighted in 1981 (Richards et al, 1993). None of the possible causal agents proposed at that time was considered to be particularly compelling (Tyler and Davies 1985), and there has been no subsequent elucidation.
Although there were isolated suggestions in the early 1980s that there had been declines in other species (eg. the Green-thighed Frog Litoria brevipalmata and the Yellow-Spotted Tree Frog L. castanea on the New England Tablelands), no verification was made. It was not until 1989, at the First World Congress of Herpetology in Canterbury, England, that there was any perception of a significant pattern of declines on a global basis, and any recognition of the desirability of taking steps to ensure the survival of amphibians.
The Action Plan for Australian Frogs is the first attempt to provide a comprehensive assessment of the conservation status and needs of Australia's frogs, and to estimate the costs of the required conservation research and management. The Action Plan suffers from a fundamental deficiency of biological information when compared with the Action Plans developed for marsupials and birds, and also by the fact that there are relatively few herpetologists in Australia with experience sufficient to generate the information required.
There is an urgent need to raise the level of commitment to the conservation of frogs and frog habitats by wildlife conservation agencies, and the level of awareness about the fauna in the general community.
Fauna surveys and frog habitat description, monitoring and protection need greater attention. Increased investigation into little known species, including those of the semi-arid zone, such as Cyclorana and Neobatrachus species, is needed to adequately assess their status.
In the early stages of the preparation of this Action Plan, a questionnaire on the issue of declining frog species (titled FROGWATCH) was circulated Australia-wide. 6,000 questionnaires were returned, principally from the highly populated peripheral regions of the continent. At most localities an overwhelming majority of respondents considered that there had been significant declines in frog populations in the area where they lived or worked. There was, however, an apparent geographic trend in the responses. In the northern half of Western Australia and the eastern Northern Territory there was little or no evidence of declines (however, the sample size from these areas was too small to draw conclusions), and it was in the south (and particularly the south-east) that most concerns were expressed.
As estimated in the following species recovery outlines, the average cost of conserving the 27 endangered or vulnerable species (Appendix 2) over the next five years is $185,900 and the total estimated cost is $5.04 million.
The use here of the categories 'Endangered', 'Vulnerable' and 'Insufficiently Known' follows their use since 1984 by the World Conservation Union (IUCN) with minor additions to the endangered and vulnerable categories. These modified definitions were provided by the Endangered Species Program (ESP) and have been used in recent years by the Australian and New Zealand Environment and Conservation Council (ANZECC). The criteria developed by Mace and Lande (1991) were recommended by the ESP for testing in this Plan, but proved unsuitable because of the inadequate data available on Australian amphibians. The 1994 IUCN criteria, developed through international debate on the need for more objective assessments of the conservation status of species, were not adopted in time for use in this Action Plan. Consequently the 1984 IUCN criteria were retained, and are as follows:
Species not located in the wild during the past 50 years, or species that have not been found in recent years despite thorough searching.
Species in danger of extinction and whose survival is unlikely if the causal factors continue to operate. Included are taxa whose numbers have been reduced to a critical level or whose habitats have been so drastically reduced that they are deemed to be in immediate danger of extinction. Also included are taxa that may now be extinct but have definitely been seen in the wild during the past 50 years and have not recently been subject to thorough searching.
Species not yet considered endangered, but likely to become so if the causal factors involved continue to operate. Included are species of which most or all of the populations are decreasing because of over-exploitation, extensive destruction of habitat or other environmental disturbance.
As applied here, these are taxa for which there are reports of local declines or extinction of populations, but the overall status of the species remains unknown. Also included are species known only from type specimens and not subsequently collected, as well as species not sighted for substantial periods. Hence, each is suspected of being endangered or vulnerable but data are inadequate to resolve the status.
Because of the paucity of information on these species, recovery outlines for them cannot be prepared, nor is it clear whether they need recovery action. To encourage further awareness of them, they are listed in Appendix 3. Any information arising from surveys or other research may contribute to knowledge of the status and potential threats to the future security of these species.
There has been considerable divergence amongst respondents and reviewers of the term 'Insufficiently Known'. The inclusion of Uperoleia marmorata is a good example. This species was collected in a remote area of the Kimberley Division of Western Australia more than 150 years ago. All subsequent reports of the species are incorrect because they involve
mis-identification of specimens collected elsewhere. Despite the remoteness of the locality, the absence of a sighting for such a long period of time is a matter of concern.
Uperoleia orientalis is also included as 'Insufficiently Known', but for different reasons: the type locality is imprecise and several attempts to locate it in the vicinity have not been successful. To exclude it from this Action Plan would permit the false assumption that it can be assumed to be 'secure' in conservation terms, and therefore not requiring conservation assessment or management.
A further problem of interpretation involves small populations of limited geographic distribution. They may be susceptible to fire or other disturbance, but if considered to be currently stable are excluded from attention here.
'Threatened' is used as a generic term, covering both endangered and vulnerable species.
The taxonomy used here retains the use of the family Leptodactylidae instead of family Myobatrachidae favoured by some herpetologists, and now used by the Census of Australian Vertebrate Species (CAVS). In the absence of greater consensus, the older name has been retained, for reasons outlined previously (Tyler 1979).
Appendix 1 lists all known named Australian frogs. Where there is disagreement about the common name, the most widely used names have been provided.
An enormous array of human activities impinge upon the viability of frogs. Those summarised in Tyler (1994) include:
- Insecticide use in agricultural and horticultural areas, particularly aerial spraying.
- Land reclamation by drainage in wetland areas, resulting in loss of breeding sites.
- The conversion of temporary ponds to dams for stock use resulting in the destruction of peripheral sheltering sites.
- Introduction of the Mosquito Fish Gambusia holbrooki which preys on frog eggs and tadpoles.
Other factors being considered as potentially implicated in frog declines include: global changes to air and water quality, increased exposure to ultra-violet radiation caused by depletion of the ozone layer, habitat modification, impacts of introduced species, pollution, hormonally active pesticide residues, pathogens and disease, acidification and climate change, including changes in climatic extremes.
While some local losses of frogs can be attributed to specific causes (such as drainage of wetlands), there are many disappearances that cannot be explained, and examples such as Eungella_Rheobatrachus vitellinus, in Eungella National Park of Queensland, defy any reasonable explanation. This species existed in creeks that were difficult to access and which were not subjected to any human pressure. In the case of R. silus and Taudactylus diurnus in the Conondale and Blackall Ranges, a portion of their habitat was less secure, and siltation resulting from an inadequate streamside buffer zone during adjacent forestry operations would have eliminated a portion of habitat. Nevertheless, this activity was not responsible for their total disappearance there, nor from the isolated Kondalilla National Park, or the headwaters of Kilcoy Creek.
As most frog species are susceptible to dehydration, it is possible that the recent decline of some populations may be attributable to drought. In the case of the stream-dependent species Rheobatrachus silus, drought would seem the most likely option to explain its demise. However there is no evidence that the disappearance of R. silus was linked to any extreme reduction in rainfall or available surface water.
Experience elsewhere in Australia and overseas rarely supports the concept that drought has been instrumental in major declines. A contrary view, however, has been put by Pechmann and Wilbur (1994), and Osborne (1996) considers it may be implicated in the decline of Pseudophryne corroboree.
Direct human activities have been a significant causal factor in the decline of species, but there is no evidence that these activities have accelerated over the past 15 or so years in which declines have become so noticeable. It remains possible that the declines are the summation of long-term effects of human activities, or that there is an unknown synergism involving several factors. The existence of frogs in urban areas has been a feature of suburban life, but many suburban declines have also been noted (for example Pseudophryne australis).
It is tempting (and certainly popular) to blame chemical pollution for frog declines. Some chemicals such as herbicides are widely used and drain into waterways. At the present time, the active constituents of herbicides in common use are exposed to reasonably rigorous toxicological scrutiny during their developmental stages, and their approval for release in Australia hinges upon an assessment of their action upon non-target organisms such as frogs. However, many herbicides, such as glyphosate, are mixed with chemical dispersants which are not subject to the same scrutiny. Glyphosate is now marketed in over 100 countries.
A recent Australian study has confirmed that glyphosate-based herbicides can be actively toxic to frogs, especially to tadpoles, possibly because of the effect of the dispersant on tadpole gills (Bidwell and Gorrie 1995). The authors recommended that a list of low impact dispersants suitable for use in aquatic environments be developed. The National Registration Authority has responded to this report, and from July 1997 a total of 74 herbicide preparations are banned from use near water.
There have been reports in several south-eastern areas of increased numbers of foxes. Frogs that bask, eg. Litoria raniformis, L. aurea and L. castanea could be particularly vulnerable to such predators.
In seeking patterns to the declines detected in the last 15 years, the following observations can be made:
- Twenty-four of the twenty-seven threatened species are confined to eastern Australia.
- Of the seven riparian species in the Wet Tropics which have disappeared at upper altitudes, three remain at lower altitudes. The other four species have disappeared from all sites.
- All fossorial species in eastern Australia are considered secure.
- In south-eastern Australia every species known to bask is locally or totally in decline, although the same is not true for south-western species.
- Eighteen of the twenty seven species are continuously associated with static or running water.
Appendix 4 summarises the postulated causes of decline and the likely threats for the species included in the recovery outlines.