Area requirements for viable populations of the Australian gliding marsupial Petaurus australis

Abstract

The yellow-bellied glider Petaurus australis is an arboreal marsupial that has an extensive but patchy distribution in native eucalypt forests along the east coast of Australia. It is considered a vulnerable species due to widespread habitat loss and low population densities resulting from social groups using exclusive homeranges of 25–85 ha. Many of its populations have been reduced in size but there are no data to assess the viability of small populations. We used the computer program ALEX to conduct a preliminary population viability analysis (PVA). The objective was to determine minimum habitat areas that contain viable populations (i.e. populations that had a 95% probability of persistence for 100 years). Life history parameter values were derived from three detailed studies of this species. The model employs an environmental variable that influences breeding success to simulate environmental stochasticity. Parameter values were varied in order to conduct a sensitivity analysis. Each parameter set was simulated 100 times for a 200-year period. The model predicted that areas containing at least 150 glider groups were needed to support viable populations. The sensitivity analysis indicated that the adult mortality rate had the greatest influence on population viability. Varying the settings of the environmental variable also showed how important this component is to population vaibility and highlights the need for studies that specifically address the relationship between environmental variation and breeding success. Minimum habitat areas were estimated by determining the area of forest that could contain 150 glider groups. Areas were based on the size of a glider group homerange and the proportion of forest in an area that could be occupied. Two scenarios exist for estimating the area of forest that is occupied. In one case, all of the available habitat (usually broad areas containing a highly favoured tree species) is occupied by gliders. This equates to 9750 ha of forest. In the other case, only a proportion (28–54%) of the forest is occupied. This equates to between 18,000 and 35,000 ha of forest to contain viable populations. Such large area requirements and an extensive geographic range suggest that the yellow-bellied glider has potential for defining minimum sizes for Australia's forested conservation reserves. Using the above data, we provide a preliminary assessment of the adequacy of the size of forested conservation reserves in New South Wales.