Distribution and Habitat

Country distribution from AmphibiaWeb's database: Australia

View distribution map in BerkeleyMapper.

The distribution of Geocrinia alba is extremely restricted, fragmented, and contained within an area north and west of the Blackwood River between Margaret River and Augusta, extreme s.w. WA (Roberts et al. 1999). The extent of occurrence of the species is approximately 130 km² and the area of occupancy is less than 2.5 km² (Roberts et al. 1999). Most populations are small, with 48 of the 61 known extant populations numbering 50 individuals or less (Driscoll 1999). Long term population monitoring data, based on calling males, is available for three populations from the period 1992-1997. Populations varied in size over this period (Roberts et al. 1999) with a maximum of 121 calling males captured in 1994 at Forest Grove (Driscoll 1998). Based on current evidence, the best estimate of total adult population size for this species is twice the estimated number of males (Driscoll 1998).

Geocrinia alba is known from Leeuwin-Naturaliste NP and Forest Grove and Witchcliffe SF (Tyler 1997). Most of the species range occurs on privately owned land (Roberts et al. 1999).

Wardell-Johnson and Roberts (1993) described the biogeographic barriers separating the distributions of four allopatric species from the Geocrinia rosea complex. Both G. alba and G. vitellina occur in permanently moist sites in relatively dry and seasonal climatic zones and their distributions are separated by 9 km of lateritic uplands and narrow valleys (Wardell-Johnson & Roberts 1993). Geocrinia alba is restricted to broad U shaped drainage depressions with swampy floors within undulating to hilly country on Leeuwin Block granite and narrow V shaped valleys on laterized Perth Basin sediments (Wardell-Johnson & Roberts 1991).

Life History, Abundance, Activity, and Special Behaviors
Genetic studies (allozyme electrophoresis) show very limited gene flow between populations indicating extremely low levels of dispersal even among adjacent populations (Driscoll 1998). The genetic differences throughout the range of the species are very large, especially given the small distances between populations (maxima 18 km; Driscoll 1998). While a precise value for the rate of dispersal cannot be calculated, the conclusion that individuals do not disperse far from their natal swamp is consistent with a mark-recapture study of G. alba and G. vitellina (Driscoll 1997). Driscoll (1997) found that 90% of adult male frogs were displaced less than 20 m over one year, while the maximum displacement was 40 m. Migration rates between populations are so low that any local extinctions are unlikely to be countered in the short term by recolonisation (Driscoll 1998).

Males call from small depressions in clay under dense vegetation cover. Egg are deposited in small depressions and are often associated with calling males. Eggs hatch and the tadpoles develop in a jelly mass with no free swimming of feeding stage (Roberts et al. 1990).

Trends and Threats
Presumed to be more extensive prior to land clearing, the geographic range of G. alba is extremely small and is now severely fragmented (Roberts et al. 1999). Wardell-Johnson and Roberts (1993) estimate that 70% of creek systems suitable for breeding have been cleared since European settlement. Approximately 18% of the species geographic range is on public land (Tyler 1997) with the remaining majority occurring on privately owned land (Roberts et al. 1999). Recently, however, the state and federal government has agreed to purchase a major block of uncleared private land, "Location 83", that contains a large number of important populations (Dale Roberts personal communication). While this radically improves the prospects of this species it is still considered to be in a precarious position (Dale Roberts personal communication).

Of the 75 sub-populations known from 1983-1996, 23 (nearly 31%) have gone extinct (Roberts et al. 1999). For most cases the cause of decline was not obvious and extinctions were equally common on private and public lands (Roberts et al. 1999). However, for privately owned land, declines have been associated with vegetation clearance, as extinctions were more common at sites with adjacent cleared land which may be associated with changed hydrology, fertiliser run-off and stock grazing (Roberts et al. 1999). Fencing has been constructed around 15 populations on nine privately owned properties in an attempt to reduce damage from grazing by stock (Roberts et al. 1999).

A dramatic reduction in population size at one location has been associated with a low intensity, fuel reduction burn (Roberts et al. 1999). The observed population decline of 60% less than pre-fire estimates is consistent with average effects reported by Driscoll and Roberts (1997) for the related species G. lutea. Fuel-reduction burning in spring has been associated with a significant decline in the number of calling males of G. lutea (Driscoll & Roberts 1997). Populations had not recovered two years after fire and the short-term impact of spring fuel-reduction burns may pose a serious threat of extinction for very small populations (Driscoll & Roberts 1997). From the information available on recruitment and age at maturity for G. alba, it is expected that populations may not begin to stabilise until four years after the fire, and recovery may take substantially longer (Driscoll & Roberts 1997). Control of fire on private property needs to be achieved and advice has been distributed to relevant landholders (Roberts et al. 1999).

As there are large genetic differences between populations, many populations will need to be conserved in order to maintain genetic variation in the long term (Driscoll 1998). Maintaining many small populations is an effective way of preventing allelic loss from the species as a whole and is likely to be more effective than conserving a smaller number of large populations provided that small populations do not become extinct, which would result in loss of unique genetic variants (Driscoll 1998). The likely biogeographic history of G. alba suggests that contractions and expansions of geographic range may be a natural phenomenon, and that they play an important role in the evolution of the species (Driscoll 1998). Therefore, if evolutionary processes are to be maintained, range changes need to be accommodated in the long term. For range expansion to take effect, unoccupied swamps need to be available, and there needs to be suitable habitat between sites through which frogs can migrate (Driscoll 1998). In the mid to long term some revegetation between swamps may be necessary (D. Driscoll personal communication).

It is unlikely that declines are attributable to the introduction of novel diseases as sites with high exposure to accidental disease introduction, such as major monitoring sites, have not shown inexplicable declines that may not be also caused by other factors (Roberts et al. 1999). This species is of major concern as populations are disappearing at an alarming rate with most losses occurring on privately owned land. The likely causes of decline are isolation of populations due to land clearing and associated small population sizes exacerbated by low natural dispersal (Roberts et al. 1999).

Comments

Featured in Amazing Amphibians on 8 July 2013

References

Driscoll, D.A. (1997). ''Mobility and metapopulation structure of Geocrinia alba and Geocrinia vitellina, two endangered frog species from southwestern Australia.'' Australian Journal of Ecology, 22, 185-195.

Driscoll, D.A. (1998). ''Genetic structure, metapopulation processes and evolution influence the conservation strategies for two endangered frog species.'' Biological Conservation, 83, 43-54.

Driscoll, D.A. (1999). ''Genetic neighbourhood and effective population size for two endangered frogs.'' Biological Conservation, 88, 221-229.

Driscoll, D.A. and Roberts, J.D. (1997). ''Impact of fuel reduction burning on the frog Geocrinia lutea in south-west Western Australia.'' Australian Journal of Ecology, 22, 334-339.

Roberts, D., Conroy, S., and Williams, K. (1999). ''Conservation status of frogs in Western Australia.'' Declines and Disappearances of Australian Frogs. A. Campbell, eds., Environment Australia, Canberra, 177-184.

Roberts, J.D., Wardell-Johnson, G., and Barendse, W. (1990). ''Extended descriptions of Geocrinia vitellina and Geocrinia alba (Anura: Myobatrachidae) from south-western Australia, with comments on the status of G. lutea.'' Records of the Western Australian Museum, 14, 427-437.

Tyler, M.J. (1997). The Action Plan for Australian Frogs. Wildlife Australia, Canberra, ACT.

Wardell-Johnson, G. and Roberts, J.D. (1991). ''The survival status of the Geocrinia rosea (Anura: Myobatrachidae) complex in riparian corridors: biogeographical implications.'' Nature Conservation 2: the Role of Corridors. D.A. Saunders and R.J. Hobbs, eds., Surrey Beatty and Sons, Chipping Norton, Australia, 167-175.

Wardell-Johnson, G. and Roberts, J.D. (1993). ''Biogeographic barriers in a subdued landscape: the distribution of Geocrinia rosea (Anura: Myobatrachidae) complex in south-western Australia.'' Journal of Biogeography, 20, 95-108.

Species Account Citation: AmphibiaWeb 2013 Anstisia alba: White-bellied Frog <https://amphibiaweb.org/species/3568> University of California, Berkeley, CA, USA. Accessed Nov 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Nov 2024.

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