Distribution, habitat requirements and conservation of the cascade treefrog (Litoria pearsoniana, Anura: Hylidae)

Biological Conservation 99 (2001) 285±292

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Distribution, habitat requirements and conservation of the cascade treefrog (Litoria pearsoniana, Anura: Hylidae) Kirsten M. Parris a,b a

Australian Research Centre for Urban Ecology, Royal Botanic Gardens Melbourne, c/o School of Botany, University of Melbourne, VIC 3010, Australia b Centre for Resource and Environmental Studies, The Australian National University, Canberra, ACT 0200, Australia Received 17 February 2000; accepted 5 October 2000

Abstract Thirty-three species of Australian frogs have apparently declined in abundance since the late 1970s, some perhaps to extinction. The cascade treefrog Litoria pearsoniana, a stream-breeding frog from the forests of sub-tropical eastern Australia, was listed as an endangered species in Queensland following reports of population declines between 1978 and 1984. However, these reports were based on limited ®eld data. I conducted a strati®ed survey across the geographic and environmental range of L. pearsoniana to determine its current distribution, abundance and habitat requirements. I detected L. pearsoniana in all major areas of mesic forest within its historical range, and at 29 of 65 sites surveyed. Statistical habitat modelling demonstrated that L. pearsoniana was most likely to occur at large streams with mesic midstorey vegetation, as indicated by the presence of palms. Abundance of the species, conditional on presence at a site, increased with increasing stream size. Litoria pearsoniana appears to have recovered from earlier population declines. However, suitability of habitat for the species in extensive areas of public forest may be threatened by cattle grazing, and the associated practices of tree clearing and frequent burning. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Amphibians; Frogs; Habitat modelling; Amphibian decline; Streams; Forests; Cattle grazing; Australia

1. Introduction In the past two decades, declining amphibian populations have been observed in many parts of the world including the Americas, Australia, Britain and Europe (e.g. Osborne, 1989; Beebee et al., 1990; Czechura and Ingram, 1990; Crump et al., 1992; Fellers and Drost, 1993; Richards et al., 1993; Blaustein et al., 1994; Lips, 1998). The widespread and synchronous nature of these reports has led to formulation of the hypothesis of global amphibian decline (e.g. Blaustein and Wake, 1990; Wake, 1991). Declines or disappearances have been reported in 33 species in Australia (Campbell, 1999 and references therein). However, in many cases there are insucient baseline data on population sizes and species' distributions to con®rm and quantify apparent declines (Pechmann and Wilbur, 1994; Gillespie and Hollis, 1996).

E-mail address: [email protected]. (K.M. Parris)

The ecology of Australia's frog fauna is poorly understood. There have been few thorough, systematic surveys of individual species (Gillespie and Hollis, 1996; Parris, 1999), and only a subset of these have covered the entire geographic or environmental range of the target taxon (e.g. Osborne, 1989; Wardell-Johnson and Roberts, 1993; Hollis, 1995; Gillespie and Hollis, 1996; Osborne et al., 1996; Roberts et al., 1997; Driscoll, 1998). A survey across the range of a species is more likely to sample the environmental variation it encounters, and provide representative data on its distribution and relative abundance. Such data are needed to assess the conservation status of a species, and to construct reliable statistical models of its habitat requirements (Burgman and Lindenmayer, 1998). These types of models have recently been termed resource selection functions (Boyce and McDonald, 1999). The cascade treefrog Litoria pearsoniana (Copland; Anura: Hylidae) is a small stream-breeding frog restricted to the forests of south-east Queensland and northeast New South Wales, Australia (McDonald and Davies, 1990). It is listed as an endangered species in

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Queensland (Queensland Nature Conservation (Wildlife) Regulation 1994), but has no special conservation status in New South Wales or nationally (Commonwealth Endangered Species Protection Act 1992; New South Wales Threatened Species Conservation Act 1995). Litoria pearsoniana is currently listed as a vulnerable species with the International Union for the Conservation of Nature (IUCN, 1996). Declines in populations of the species were noted in the Blackall, Conondale and D'Aguilar Ranges in south-east Queensland (Fig. 1) between 1978 and 1984 (McDonald and Davies, 1990; Ingram and McDonald, 1993, and references therein). More recently, Laurance and colleagues asserted that populations of L. pearsoniana had declined by more than 90% across its range in south-east Queensland and north-east New South Wales, but provided no data to support this claim (Laurance, 1996; Laurance et al., 1996). This paper presents an assessment of the distribution and habitat requirements of L. pearsoniana, using data collected during a ®eld survey across the geographic range and environmental breadth of the species. Climate and habitat variables in¯uencing the presence and abundance of L. pearsoniana are investigated using logistic regression and mixed models for unbalanced data. Reports of population declines in the species are discussed, and information on its habitat requirements is used to assess potential threats to its persistence in the forests within its range.

the species occurs from the Conondale Range in southeast Queensland (approximately 26  South) to the Lismore area in north-east New South Wales (approximately 29  South; Fig. 1). Litoria barringtonensis occurs to the south of this area. 2.2. Study area The study area covered approximately 14,000 km2 of south-east Queensland and north-east New South Wales, Australia (Fig. 1). I estimated the theoretical limits of the distribution of L. pearsoniana using BIOCLIM, a bioclimatic prediction system (Busby, 1991). From point records of species presence, BIOCLIM

2. Methods 2.1. Litoria pearsoniana There has been considerable confusion surrounding the taxonomy and distribution of L. pearsoniana and three closely related species: the leaf-green treefrog Litoria phyllochroa, the Barrington treefrog Litoria barringtonensis and the peppered treefrog Litoria piperata (Donnellan et al., 1999). McDonald and Davies (1990) de®ned the distribution of L. pearsoniana as extending from the Conondale Range in south-east Queensland to the Lismore area in north-east New South Wales, with an isolated population at Kroombit Tops in mid-east Queensland (after Czechura, 1986). McGuigan et al. (1998) excluded the population at Kroombit Tops from L. pearsoniana following analysis of data from mitochondrial DNA sequencing. The most recent study of the taxonomy of this group recommended that L. barringtonensis, L. pearsoniana and the Kroombit Tops population be considered a single species containing four lineages or evolutionary signi®cant units (Donnellan et al., 1999). However L. barringtonensis and L. pearsoniana have not yet been formally rede®ned (Donnellan et al., 1999). Thus, the de®nition of L. pearsoniana used in this study follows McGuigan et al. (1998):

Fig. 1. Map of the study area in south-east Queensland and north-east New South Wales, Australia, showing the location of survey sites. The climate envelope of the cascade treefrog Litoria pearsoniana, estimated using BIOCLIM, is shown in grey. Closed circles indicate sites where the species was found, and open circles indicate sites where it was not found during the study. The areas of forest surveyed are designated as follows: BL, Blackall Range; CO, Conondale Range; DA, D'Aguilar Range; MA, Main Range; BO, Border Ranges; NI, Nightcap Range; GI, Girraween.

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summarised the climatic conditions suitable for L. pearsoniana, and identi®ed the area of Australia that experiences these conditions (the climate envelope of the species). Within the boundaries of the climate envelope, factors such as the presence of suitable habitat, interactions with other species, historical events and disturbance will in¯uence the actual distribution of L. pearsoniana. Since European settlement, areas of lowland forest within the potential range of L. pearsoniana have been cleared for agriculture, and the species is restricted to the remaining forests which are largely in mountainous terrain (Parris and Norton, 1997). As de®ned in this study, L. pearsoniana does not occur south of approximately 29 South, despite the presence of suitable climatic conditions (Fig. 1). 2.3. Selection of survey sites In order to sample the environmental variation encountered by L. pearsoniana, I strati®ed the survey on three variables: mean temperature of the warmest quarter (MTWQ), average precipitation of the warmest quarter (PWQ), and stream size. Litoria pearsoniana is most active, and thus most likely to be in¯uenced by ambient temperature and moisture, during the warmest quarter of the year. The study area was divided into 14 climate classes, each de®ned by a unique combination of MTWQ and PWQ, and each class was sampled during the survey (Table 1). Sites were also selected to represent the variation in stream size within the range of L. pearsoniana (Table 1), as Parris and McCarthy (1999) found a signi®cant relationship between stream size and the richness and composition of frog assemblages at forest streams in south-east Queensland. Stream size was measured from the average annual volume of precipitation in the catchment (watershed) upstream of the survey site. Upstream catchment volume (in gigalitres; GL) was calculated by multiplying the catchment area upstream of the site, measured from topographic maps, by the annual mean precipitation in the catchment estimated using BIOCLIM. Upstream catchment volume was calculated for all sites except one, which was located on a section of stream that ¯owed underground. Where di€erent broad forest types were shown on topographic maps, sites were chosen in each forest type where possible. A total of 65 sites were selected for survey (Fig. 1; Table 1) in nine State Forests and eight National Parks, and in one instance, on private land. Sites were 1 ha in size, and included a 100 m transect of stream and 50 m either side. They were located >1 km apart if in di€erent catchments, and >4 km apart if in the same catchment, in an e€ort to ensure statistical independence. The majority of the forests surveyed were in mountainous terrain, where it was assumed that frogs were more likely to travel within catchments than between catchments.

287

2.4. Frog surveys Two sampling techniques were used during the frog survey: nocturnal stream searches and automatic recording of frog calls (Parris et al., 1999). Nocturnal searches involved walking along a stream transect, spotlighting for frogs with head lamps and counting and recording frog advertisement calls. When necessary for identi®cation, frogs were caught, photographed, then released. A minimum of one person hour was spent searching each site. The automatic tape recorders, established at the mid-point of the 100-m stream transect, started at 1800 h (approximately 1 h before sunset), recorded for 1 min (January±March 1995) or 30 s and then turned o€ for 12 min. This cycle was repeated until midnight, giving 27 or 13.5 min of recording for each tape recorder each night. Sites were surveyed for frogs in eight periods over ®ve breeding seasons between 1995 and February 1999. Each of the 65 sites was surveyed a minimum of four times, in most cases twice with nocturnal searches and twice with automatic tape recorders. I recorded presence and number of individuals detected at a site for all frog species encountered during the survey. 2.5. Vegetation and habitat surveys Detailed surveys of the structure and composition of the vegetation, stream characteristics and disturbance were undertaken at all sites. Broad forest type, stream Table 1 Distribution of the 65 survey sites across 14 climate classes and four classes of stream sizea Climate PWQ class (mm)

MTWQ LCV<3 LCV 3±4 LCV 4±5 LCV>5 Total (GL) (GL) (GL) (GL) ( C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

420 20422 22424 420 20422 22424 24426 420 20422 22424 24426 420 20422 22424

Total a

2004400 2004400 2004400 4004600 4004600 4004600 4004600 6004800 6004800 6004800 6004800 >800 >800 >800

1

5

1 2 5 1

15

1 3 2 7 7 2 2 8

1

2 7

1

1

2 1 2 37

11

1

2 4 1b 2 14 14 3 I 5 13 1 2 1 2 65

Each climate class was de®ned by a unique combination of precipitation of the warmest quarter (PWQ) and mean temperature of the warmest quarter (MTWQ). Stream size was measured by the mean annual volume of precipitation in the catchment (watershed) upstream of the site (upstream catchment volume). LCV=Log10 (upstream catchment volume). b Upstream catchment volume was not calculated for this site, which was located on a section of stream that ¯owed underground.

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slope, stream size (measured by upstream catchment volume), latitude, longitude, elevation, precipitation of the warmest quarter and mean temperature of the warmest quarter were determined for each site. Five forest types were recognised on the basis of the combination of trees in the overstorey: dry sclerophyll forest; dry sclerophyll to wet sclerophyll forest; wet sclerophyll forest; wet sclerophyll forest to rainforest; and rainforest. The overstorey of wet sclerophyll forest to rainforest contained a mixture of rainforest trees, Eucalyptus spp. and/or brush box Lophostemon confertus, while that of rainforest contained rainforest species only. The following habitat variables were measured in the riparian zone: species composition of the understorey vegetation; structure, complexity and density of the understorey and midstorey vegetation; presence of palms in the midstorey; and % cover of the understorey, midstorey and overstorey vegetation. Stream width and stream substrate (rock or silt/sand) were measured at the mid-point of the transect. Any evidence of disturbance in the whole 1-ha site was recorded, and an additive disturbance index calculated. Disturbance by wind, cattle and pigs, selective logging, presence of unsealed tracks, evidence of ®re more than three years ago, moderate infestations of weeds and recent ¯ooding each contributed one point to the disturbance index. Partial clearing, ringbarking, evidence of recent ®re, presence of sealed roads and heavy infestations of weeds each contributed two points. 2.6. Data analysis Logistic regression (Hosmer and Lemeshow, 1989) was used to estimate the probability of occurrence of Litoria pearsoniana at a site as a function of climate and habitat variables. Because the survey e€ort (nights of survey) varied between sites, the number of times the species was detected at a site was expressed as a proportion of the number of times the site was surveyed. The binomial distribution is an appropriate distribution for these data, and logistic regression is an appropriate analysis for binomial data (Hosmer and Lemeshow, 1989). Non-automated backwards elimination of variables was used for selection of the ®nal model. Highly correlated explanatory variables (r>0.4) were not included in the same model. The signi®cance of explanatory variables was determined from the change in deviance statistic, and non-signi®cant variables were excluded from the model. I allowed for potential over-dispersion in the models by scaling the change in deviance statistics and standard errors by the residual mean deviance. Diagnostic plots for the model were checked to ensure that the assumptions made were reasonable. Data on the abundance of L. pearsoniana were only available from nocturnal searches, as automatic tape recorders did not provide reliable estimates of the number

of animals active during a survey. Thus, I modelled the number of L. pearsoniana detected with stream searches on a visit to a site, conditional on detection of the species with any method, using mixed models for unbalanced data (Searle et al., 1992). Abundance data were log transformed prior to analysis. The models accounted for the structure in the data by including random e€ects at the visit and site level (i.e. variation between visits to the same site and variation between sites), estimated by restricted maximum likelihood estimation (REML), and ®xed e€ects at the site level (habitat variables), estimated by ordinary least-squares regression. 3. Results 3.1. Distribution of L. pearsoniana L. pearsoniana was present in all major areas of forest surveyed, except for the dry sclerophyll forests of Girraween National Park (Fig. 1). Girraween is an historical locality for the species, on the western margin of its geographic range and the driest margin of its climatic range. L. pearsoniana was detected at 29 of the 65 sites surveyed, an occurrence rate of approximately 45%. This was the second highest rate of occurrence of the 26 species of native frogs detected during the survey. Only the great barred frog Mixophyes fasciolatus, a common and widespread species, was encountered more frequently. The sites where L. pearsoniana was detected ranged in elevation from 120±800 m, in latitude from 26.53±28.49 South, and in longitude from 152.37±153.36 East (Fig. 1). The species was only found at sites with average precipitation of the warmest quarter >420 mm, and mean temperature of the warmest quarter between 19.5 and 23.9 C. I detected L. pearsoniana at streams with an upstream catchment volume ranging from 158 to 50,120 GL, although 27 of 29 records were from larger streams (upstream catchment volume >1000 GL). 3.2. Habitat requirements of L. pearsoniana L. pearsoniana was most likely to occur at large streams with mesic mid-storey vegetation in the riparian zone, as indicated by the presence of palms (Table 2; Fig. 2). Where palms were present, the predicted probability of occurrence of L. pearsoniana ranged from 0.02 (95% CI=0.004±0.074) at streams with an upstream catchment volume of 100 GL, to 0.89 (0.72±0.97) at streams with an upstream catchment volume of 63,100 GL. At sites without palms in the midstorey, the predicted probability of occurrence ranged from 0.002 (0.0003±0.02) to 0.52 (0.20±0.83) over the same range of stream sizes (Fig. 2). The largest number of individuals of L. pearsoniana found on a visit to a site was approximately 50. At sites

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where L. pearsoniana was present, its predicted abundance increased with increasing stream size (Fig. 3). The REML model of abundance of the species predicted an average of one individual per visit at a site with an Table 2 Results of logistic regression analysis of the probability of occurrence of the cascade treefrog Litoria pearsoniana as a function of stream size (measured by upstream catchment volume) and the presence or absence of palms in the midstorey vegetationa Variable Constant Log10 (upstream catchment volume) Presence of palms

Estimate

S.E.

P

10.48 2.204 2.037

1.89 0.451 0.696

± <0.001 <0.001

289

upstream catchment volume of 280 GL, increasing to 10 individuals at a site with an upstream catchment volume of 45,900 GL (Fig. 3). Estimates of the components of variance from the abundance model indicated that the intra-site (between-visit) correlation was very low (r= 0.045). Thus, at a site where the species was present, the number of individuals detected on one visit bore little relationship to the number detected on another. This has important implications for interpretation of data from surveys for L. pearsoniana, particularly those with only a small number of visits to each site. 4. Discussion

a

The estimate of the coecient, the standard error and the statistical signi®cance are shown

4.1. Habitat requirements In forests within its climatic range, L. pearsoniana is most likely to occur at large streams with mesic midstorey vegetation, indicated by the presence of palms. For successful breeding, L. pearsoniana requires a stream that is large enough to hold water for a sucient length of time for its tadpoles to develop to metamorphosis (2±2.5 months under laboratory conditions; McDonald and Davies, 1990). Even during the wet season, the smaller streams in the study area are regularly dry, ¯owing only for short periods after heavy rainfall. The species richness of frog assemblages at forest streams in the Blackall and Conondale Ranges, southeast Queensland, increases with increasing stream size (Parris and McCarthy, 1999), indicating that larger streams are more likely to provide suitable habitat for other frog species in the region as well.

Fig. 2. Logistic regression model of the probability of occurrence of the cascade treefrog Litoria pearsoniana as a function of stream size, measured by upstream catchment volume (P<0.001), and the presence or absence of palms in the midstorey vegetation (P<0.001). Dashed lines represent the 95% con®dence intervals.

Fig. 3. Mixed (estimated by restricted maximum likelihood; REML) model of the abundance of the cascade treefrog Litoria pearsoniana on a visit to a site, conditional on presence, as a function of stream size, measured by upstream catchment volume (P<0.001).

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The density and composition of riparian vegetation can be important correlates of habitat suitability for amphibian species (e.g. Evans et al., 1996; Gillespie and Hollis, 1996; Pyke and White, 1996; Munger et al., 1998). Palms such as picabeen Archontophoenix cunninghamiana and walking stick palm Linospadix monostachya are associated with mesic vegetation and a moist microclimate in the lower strata of the forest (Cronin, 1989). During the breeding season, adults of L. pearsoniana shelter diurnally under logs, rocks and leaf litter and in moist holes close to the stream (McDonald and Davies, 1990). Males call from vegetation adjacent to or within streams, including palms, sedges, overhanging tree branches and ferns. Studies of breeding success and adult survival at streams with mesic and xeric riparian vegetation would help to clarify the causal mechanisms for the observed relationship between the presence of L. pearsoniana and mesic midstorey vegetation. 4.2. Conservation status Supporting data for reported declines of populations of L. pearsoniana between 1978 and 1984 are few and largely unpublished. This precludes their evaluation with respect to the extent of survey and the sampling e€ort involved in their collection. There are limited data indicating a possible decline in parts of south-east Queensland during this period (McDonald and Davies, 1990; Ingram and McDonald, 1993), but there are no data, either published or unpublished, to support a decline in north-east New South Wales (cf Laurance, 1996; Laurance et al., 1996). During the present study, L. pearsoniana was relatively common and easy to detect at suitable forest streams. This is consistent with results of other recent surveys in sections of its range (Hines et al., 1999; Goldingay et al., 1999). There are two possible explanations for the available data. Firstly, L. pearsoniana did su€er population declines, and has subsequently recovered. Secondly, populations of L. pearsoniana did not decline substantially, but data collected during localised and unsystematic surveys presented a misleading picture of the status of the species. The number of L. pearsoniana active at a site varies markedly from night to night (Fig. 3), and surveys that include only a small number of visits to each site may furnish unreliable estimates of the abundance of the species. Field data collected during this study and the resulting models of the habitat requirements of L. pearsoniana provide a reliable description of the current distribution and abundance of the species, against which future changes can be assessed. 4.3. Threatening processes Although L. pearsoniana is currently present in forests throughout most of its historical range, its continued

persistence could be threatened by a number of processes. These include disease caused by a water-borne chytrid fungus, clearing and urban development upstream of forest areas, timber harvesting, the spread of weeds such as mist weed Eupatorium riparium and lantana Lantana camara, and damage to streams and riparian areas by cattle and feral pigs (Parris and Norton, 1997; Berger et al., 1998; Hines et al., 1999). The observed relationship between the presence of Litoria pearsoniana and mesic midstorey vegetation in the riparian zone supports the exclusion of cattle grazing, and the associated practices of tree clearing and frequent burning, from public forests. These practices alter the light and moisture regimes in the lower strata of the forest, and dramatically change the structure and composition of the understorey and midstorey vegetation (Anonymous, 1998, and references therein). This results in a more open forest with a simple, xeric understorey and midstorey dominated by grass and weeds (Leigh and Holgate, 1979; Pettit et al., 1995), which, on the basis of the current study, is less suitable as habitat for L. pearsoniana. Furthermore, cattle tend to congregate around streams, using them as watering points or sheltering in the riparian forest. Trampling of riparian areas by cattle leads to deterioration of water quality, erosion of stream banks and channels, and changes in stream morphology (Armour et al., 1991; Trimble and Mendel, 1995; Borsboom, 1996). Currently 53% of State Forests and 76% of Timber Reserves (by area) in south-east Queensland are leased for cattle grazing (Anonymous, 1998). Cattle are also grazed in some areas of public forest in north-east New South Wales. 4.4. Assessment of amphibian declines The survey method demonstrated in this paper, involving repeat sampling at replicated survey sites representative of the environmental variation experienced by the target taxon, could be used to assess the status of other amphibian species that have apparently declined in recent decades. Changes in the relative abundance or probability of occurrence of a species over time could be identi®ed by comparing data from later surveys to the statistical models of its habitat requirements constructed using the original data set (e.g. Cox, 1958; Miller et al., 1991). Reliable ®eld data are needed to establish baseline information on the distribution and relative abundance of poorly known species, to clarify the extent and pattern of population declines, and to identify the life history attributes that may predispose a species to decline (e.g. Williams and Hero, 1998). This will reduce uncertainty regarding the magnitude and causes of declines, and help us to ®nd practical solutions for conservation of amphibians.

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Acknowledgements I thank Michael McCarthy, Peter West, Derek Cleland, Ursula Grott, Denise Elias, Adrian Caneris, Greg Czechura, Tony Norton, Scott Osborn, Wyn Boon, Randall Donohue, Natasha West, Andrew Howley, Harry Hines, Anthony Overs and Rodney Anderson for their assistance in the ®eld. Ross Cunningham and Christine Donnelly provided valuable advice on survey design and assistance with statistical analysis. I thank Andrew Claridge, Glen Ingram, Helen Neave, Henry Nix, Tony Norton and Will Osborne for their assistance during this study. Frank Lemckert, Keith McDonald, The Queensland Museum and The Australian Museum provided frog records for the BIOCLIM analysis. Jim Brown and Michael McCarthy provided helpful comments on the manuscript. This study was approved by the ANU animal experimentation ethics committee, and conducted under the following permits: QDPI permits No. 788, 860, and 919, QNPWS permit No. 2001, QDNR permit Nos. 1188 and 1301, QDEH permit Nos. HO/000139/95/SAA and E5/000003/98/SAA, NSW NPWS scienti®c investigation license No. B 1474 and SF NSW permit Nos. 5267 and 5269. References Anonymous, 1998. Forest Grazing. Queensland CRA/RFA Steering Committee, Queensland and Commonwealth Governments, Brisbane. Armour, C.L., Du€, D.A., Elmore, W., 1991. The e€ects of livestock grazing on riparian and stream ecosystems. Fisheries 16, 7±11. Beebee, T.J.C., Flower, R.J., Stevenson, A.C., Patrick, S.T., Appleby, P.G., Fletcher, C., Marsh, C., Natkanski, J., Rippey, B., Battarbee, R.W., 1990. Decline of the natterjack toad Bufo calamita in Britain: palaeoecological, documentary and experimental evidence for breeding site acidi®cation. Biological Conservation 53, 1±20. Berger, L., Speare, R., Daszak, P., Green, D.E., Cunningham, A.A., Goggin, C.L., Slocombe, R., Ragan, M.A., Hyatt, A.D., McDonald, K.R., Hines, H.B., Lips, K.L., Marantelli, G., Parkes, H., 1998. Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America. Proceedings of the National Academy of Sciences 95, 9031±9036. Blaustein, A.R., Hokit, D.G., O'Hara, R.K., Holt, R.A., 1994. Pathogenic fungus contributes to amphibian losses in the Paci®c Northwest. Biological Conservation 67, 251±254. Blaustein, A.R., Wake, D.B., 1990. Declining amphibian populations: A global phenomenon? Trends in Ecology and Evolution 5, 203±204. Borsboom, A., 1996. A forest for frogs. Wildlife Australia Spring 1996, 26±29. Boyce, M.S., McDonald, L.L., 1999. Relating populations to habitats using resource selection functions. Trends in Ecology and Evolution 14, 268±272. Burgman, M.A., Lindenmayer, D.B., 1998. Conservation Biology for the Australian Environment. Surrey Beatty, Chipping Norton. Busby, J.R., 1991. BIOCLIM Ð a bioclimate analysis and prediction system. In: Margules, C., Austin, M. (Eds.), Nature Conservation: Cost E€ective Biological Surveys and Data Analysis. CSIRO, Canberra, pp. 64±68.

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