Ecology and Conservation Biology of the Baw Baw Frog Philoria frosti (Anura: Myobatrachidae): Distribution, Abundance, Autoecology and Demography Gregory J. Hollis Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy January 2004 Department of Zoology University of Melbourne Abstract The decline of amphibian populations around the world is a well documented phenomenon. The Baw Baw Frog Philoria frosti belongs to a group of high-elevation, mountain-top amphibians in Australia that have undergone recent population declines, but an understanding of the responsible agents is deficient or absent for most species. The inability to diagnose agents of decline has mostly been attributed to a paucity of knowledge on the natural history of these species. The discipline of conservation biology provided a scientific basis for commencing investigation into the decline of P. frosti. This thesis examines the pattern and extent of decline, and the autoecology and demography of the species, in order to provide a basis for evaluating conceivable decline-agents, and to establish a platform to commence diagnosis of the decline. The results of comprehensive surveys confirm that the population of P. frosti has undergone a significant decline and contraction in range at sub-alpine elevations (> 1300 m), and may have also declined at lower, montane elevations (960 – 1300 m) where previously unknown populations were recorded on the south-western and north-eastern escarpment of the Baw Baw Plateau. The results of monitoring between 1993 – 2002 indicate a continuation of the decline of P. frosti at elevations above 1400 m, whilst populations between 960 and 1400 m appear to have remained relatively stable. Due to a lack of historical base-line data, it is not known if populations from montane elevations have declined to the same extent as at sub-alpine elevations. The survey technique involving counts of calling males was investigated for its aptness in estimating and monitoring the abundance of P. frosti. The species rarity and cryptic nature, and its occupancy of a harsh climate in a landscape that is difficult to negotiate, excluded other potentially useable survey techniques. Participation by calling males during the breeding season was found to vary daily and seasonally. If not accounted for, this temporal variation can result in under- estimation of abundance. Extreme climatic conditions was also found to reduce the detectability of calling males during surveys. Retrospective power analyses indicate that sufficient effort was attained to detect changes in population size of less than 10% at all elevations examined, except for some subsets of data that comprised a small number of survey transects. A thorough examination of the distribution and abundance of P. frosti showed that the highest density of calling males occurred on the south-western escarpment of the Baw Baw Plateau between 1300 and 1400 m, followed by populations between 960 and 1300 m. The lowest density of males occurred at elevations above 1400 m, and on the north-eastern escarpment between 1200 and 1400 m. The size of the adult male population was estimated to be 7000 individuals. iii Habitat attributes from extant breeding locations of P. frosti were compared with those from randomly-selected locations chosen within the known domain of potential breeding habitat of the species. A significant difference was recorded between extant and random sites, as determined from attributes recorded at different scales. Particular biophysical and floristic attributes, and associated environmental gradients, were found to be correlated with the differences observed. Breeding habitats located within topographically protected, cool, moist communities on the south- western escarpment of the Baw Baw Plateau appear to represent the core breeding habitat of the extant population. The results suggest that historical populations of P. frosti observed prior to this study were less selective in their preference for breeding habitat compared to extant population, following the decline of the species. Examination of male calling behaviour over several breeding seasons revealed annual, seasonal and temporal differences in calling activity and participation rates. Additional variation in the call structure of the species is described and quantified. Climatic variation, due to differences in habitat structure and elevation, was shown to influence duration, timing, rate and variance of calling activity. Calling activity was also shown to occur within a relatively narrow climatic window, indicating that reproductive activity may be particularly sensitive to natural or anthropogenic influences. Radio-tracking revealed that adult P. frosti are relatively sedentary over breeding and post- breeding seasons, but partake in a consistent pattern of movement from aquatic to adjacent, terrestrial habitats following oviposition (females), and at the conclusion of calling activity (males). Extent and probability of movement was shown to be influenced by weather conditions, with overall movement being confined to a narrow range of climatic conditions. Movement activity was found to mostly occur when external climate conditions (ambient temperature) mimicked those experienced by frogs at sheltering sites (substratum temperature). These climatic constraints on movement and dispersal by P. frosti have implications for the management of land use within the habitat of the species. Skeletochronological techniques were successfully used to determine longevity, maturation and growth in P. frosti individuals. The cryptic nature and rarity of the species precluded other methods as being suitable for acquiring this information. The species is relatively long-lived, and attains sexual maturity at an older age when compared to most other anurans. A skewed age-class distribution of adult samples from the extant population indicated population instability when compared to the binomial age-class distribution of museum samples examined. The dominance of younger-aged adults following the decline of the species suggests a decline-agent that has impacted on the post-metamorphic stage of the population. Knowledge gained in this study has enabled identification of the most conceivable agents of decline for P. frosti. Information acquired on the ecological requirements of the species, and iv subsequent inference of sensitivity to natural and anthropogenic influences, has contributed to progress towards the development of a conservation strategy for the species, as well as providing input into designing research programs to assess the potential impact of land management. v Declaration This is to certify that i. The thesis comprises only my original work towards the PhD except where indicated in the preface, ii. Due acknowledgment has been made in the text to all other material used, iii. The thesis is less than 100,000 words in length exclusive of tables, maps, bibliographies and appendices. -------------------------------- Gregory J. Hollis Department of Zoology University of Melbourne, Parkville vii Preface This thesis is structured as a sequence of five chapters that present primary data (3 – 7), accompanied by chapters comprising general introduction (1), review of existing information on P. frosti and general methods (2) and synthesis and conclusions (8). Population survey data examined from three years (1993 - 1995) in Chapter 3 were collected by myself and an assistant prior to candidature, the results from 1993 and 1994 being published in Hollis (1995). I was also assisted in the field during population surveys (1996 – 2002) by numerous people (names are included in acknowledgment section) for reasons of logistics, safety, and the narrow time-frame within which to conduct an annual survey of the species. John Davies assisted in collection, identification and interpretation of botanical and soil data for analysis in Chapter 4, under my supervision. Ordination analyses in Chapter 4 were carried out in collaboration with Peter Minchin. Peter Minchin also modified the algorithm used to derive Bray- Curtis dissimilarity coefficients within DECODA software to incorporate more detailed examination of habitat profiles (referred to as ‘height-difference-weighted Bray-Curtis’). This modified dissimilarity coefficient is cited as Minchin (unpublished). Peter Minchin, John Davies and myself intend to publish a paper based on the contents of Chapter 4, with myself as senior co- author. Diagrams depicting kernel distributions for home range analyses in Chapter 6 were constructed in collaboration with Rolf Willig. The laboratory work, and some of the field work, on which Chapter 7 is based, was carried out jointly by Michael Scroggie and myself. Both myself and Michael Scroggie intend to publish a paper based on the contents of Chapter 7, with myself as senior co-author. Research from this thesis has contributed to the publication of a paper (Osborne et al. 1999), cited elsewhere in this thesis. ix Acknowledgments My sincere thanks goes to my supervisors Graeme Watson and Graeme Coulson for their encouragement, advice and guidance throughout this study. I am also particularly grateful to friends and colleagues, Graeme Gillespie, John Davies, David Hunter, Michael Scroggie, Gerry Marantelli, Peter Robertson and Murray Littlejohn for their support, advice and stimulating discussions on amphibian ecology, conservation biology and botany over the duration of this study. There are numerous friends, colleagues and helpers