MODELING THE INTERRELATIONSHIPS BETWEEN HABITAT PATCHINESS, DISPERSALCAPABILITY AND METAPOPULATION PERSISTENCE OF THE ENDANGERED SPECIES, LEADBEATERS POSSUM, IN SOUTH-EASTERN AUSTRALIA

A computer simulation model was used to derive estimates of the probab ility of extinction of populations of the endangered species, Leadbeat er's Possum (Gymnobelideus leadbeateri), inhabiting ensembles of habit at patches within two wood production forest blocks in central Victori a, south-eastern Australia. Data on the habitat patches were extracted from forest inventory information that had been captured in the datab ase of a Geographic Information System (GIS). Our analyses focussed on a range of issues associated with the size, number and spatial config uration of patches of potentially suitable habitat that occur within t he Ada and Steavenson Forest Blocks. The sensitivity of extinction ris ks in these two areas to variations in the movement capability of G. l eadbeateri was also examined. Our analyses highlighted major differenc es in the likelihood of persistence of populations of G. leadbeateri b etween the Ada and Steavenson Forest Blocks. These were attributed to differences in the spatial distribution and size of remnant old growth habitat patches as well as the impacts of wildfires. In addition, sim ulation modelling revealed a different relative contribution of variou s individual patches, and ensembles of patches, to metapopulation pers istence in the two study areas. In those scenarios for the Ada Forest Block in which the impacts of wild-fires were not modelled, our analys es indicated that a few relatively large, linked patches were crucial for the persistence of the species and their loss elevated estimates o f the probability of extinction to almost 100%. A different outcome wa s recorded from simulations of the Steavenson Forest Block which, in c omparison with the Ada Forest Block, is characterized by larger and mo re numerous areas of well connected patches of old growth forest and w here we included the impacts of wildfires in the analysis. In this cas e, metapopulation persistence was not reliant on any single patch, or small set of patches, of old growth forest. We found that in some circ umstances the probability that a patch is occupied whilst the metapopu lation is extant may be a good measure of its value for metapopulation viability. Another important outcome from our analyses was that estim ates of extinction probability were influenced both by the size and th e spatial arrangement of habitat patches. This result emphasizes the i mportance for modelling metapopulation dynamics of accurate spatial in formation on habitat patchiness, such as the data used in this study w hich were derived from a GIS. The values for the predicted probability of extinction were significantly influenced by a range of complex int er-acting factors including: (1) the occurrence and extent of wildfire s, (2) the addition of logging exclusion areas such as forest on steep and rocky terrain to create a larger and more complex patch structure , (3) estimates of the quality of the habitat within the logging exclu sion areas, and (4) the movement capability of G. leadbeateri. Very hi gh values for the probability of extinction of populations of G. leadb eateri were recorded from many of the simulations of the Ada and Steav enson Forest Blocks. This finding is the result of the limited areas o f suitable old growth forest habitat for the species in the two areas that were targeted for analysis. Hence, there appears to be insufficie nt old growth forest in either of the two forest blocks to be confiden t that they will support populations of G. leadbeateri in the long-ter m, particularly ifa wildfire were to occur in the next 150 years. The results of sensitivity analyses indicated that estimates of the probab ility of extinction of G. leadbeateri varied considerably in response to differences in the values for movement capability modelled. This hi ghlighted the need for data on the dispersal behaviour of the species.