Squirrel Glider Population Viability Assesment
		Paper by: Dr. Andrew Smith Austeco Environmental Consultants 84 Brown Street Armidale NSW 2350 austeco@tpgi.com.au
	Assessing the viability of threatened species populations under tests 1 & 2 of the TSC Act 8 part test is one of the most challenging tasks facing consultant ecologists. This case study outlines procedures used to apply the 8 part test to populations of threatened Squirrel Gliders in vegetation remnants in Lake Macquarie City Council and Wyong Shire. The project brief for Lake Macquarie required an assessment of the viability of a squirrel glider population before and after clearing of a 12 ha portion of a large (> 450ha) remnant. The project brief in Wyong Shire was broader, requiring the development of models and rule sets for determining the viability of remnants of different size, habitat quality and isolation. The method involved the following steps: Map vegetation/habitat types Map and number vegetation fragments Survey of glider density in fragments stratified by size, isolation, condition and habitat type Model the effects of patch size, isolation, habitat type and condition on glider density Predict glider distribution and abundance (population size) in the regional remnant network Rank remnants according to their viability and conservation significance. Procedures 1-5 are relatively straight forward. Glider density averaged about 0.5 animals per ha. and peaked in Sydney Red Gum forest or woodland with a Banksia understorey at about 0.9 animals per hectare. The probability of glider occurrence declined significantly with remnant isolation, the size of adjacent remnants and remnant size. The resulting models were used to predict glider distribution and abundance and estimate population sizes in both study areas (over 430 in LMCC and 2800 in WS). The critical issue of determining which fragments were viable and of high conservation value and which were at risk of local extinction and of low conservation value was more problematic. For this purpose populations of gliders were considered to be at risk of local extinction where their probability of occurrence in remnants falls below 100%. Remnant size was found to be the most practical predictor of population viability after consideration of isolation and size of adjacent remnants. The smallest remnant size with a 100% probability of glider occurrence was 128 ha, an area large enough to support about 60 individuals. Patches of less than 12 ha had only a 50% probability of glider occurrence unless they were close to other larger patches. A fragmentation index which combined patch size, patch isolation and size of adjacent patch was developed to predict viability of habitat remnants (scores of 4 or higher are considered viable). Using this index fragments as small as one hectare are viable if close to larger remnants and but fragments have to exceed 90 hectares to be viable if completely isolated. For the purpose of applying the 8 point test it is recommended that: Any clearing that reduces a threatened species probability of occurrence below 100% be considered significant; Any clearing of habitat that has less than a 50% probability of species occurrence be considered insignificant; and Any proposed clearing of remnants between the 100% and 50% levels be evaluated on individual merit. As these viability targets apply only to areas isolated in the short term (approximately 50 years post clearing) it is further recommended that viability limits for entire regions be set at much higher levels (2000 individuals).
Ecological Consultants Association of NSW Inc.