Ecology of greater gliders, Petauroides Volans Kerr 1792, in relation to variations in habitat quality in eucalypt forests in south-east New South Wales
L.W. Braithwaite and co-researchers hypothesised that the population density and diversity of the arboreal marsupial fauna of the eucalypt forests near Eden, New South Wales were primarily determined by the concentrations of nitrogen, phosphorus and potassium in the mature foliage of the eucalypts. I investigated this hypothesis in relation to the Greater Glider Petauroides votans. The first main objective of my study was to examine why population densities of P. votans are low in eucalypt forests with relatively low concentrations of nutrients in their mature foliage and high in eucalypt forests with relatively high concentrations of nutrients in their mature foliage. Initially, several a priori hypotheses were proposed that could account for the observed population densities of P. votans in these forests, and these were tested at two forest sites in south-eastern N.S.W. by studying and comparing the ecology of P. votans at these sites. One site of 24.6 ha at Wadbilliga carried four species of eucalypt (E. dalrympleana, E. fastigata, E. radiata, E. viminalis}. These had high concentrations of N and P in their mature foliage when compared to the range of values known for foliar N and P in this genus. The other site of 50.1 ha was at Morton and consisted of 40.3 ha of two species of eucalypts, E. gummifera and E. piperita, which formed 'forest type A'. Two smaller areas, termed 'forest types B and C', within the Morton site also supported other eucalypt species, E. sieberi at forest type B and E. consideniana, E.pellita and E. sieberi at forest type C. The nutrient concentration in the mature foliage at Morton was generally lower than at Wadbilliga. Basal area and height of the eucalypts, and the relative concentrations of N and P in their mature foliage suggested an apparent decline in forest site foliage suggested an apparent decline in forest site productivity from Wadbilliga through Morton forest types C, B and A. The change in the ratio of Symphyomyrtus to Monocalyptus eucalypts across these forests also was consistent with the presence of a decline in productivity. Many aspects of the social organisation of P. volans were related to this decline. There productivity from Wadbilliga through Morton forest types C, B and A. The change in the ratio of Symphyomyrtus to Monocalyptus eucalypts across these forests also was consistent with the presence of a decline in productivity. Many aspects of the social organisation of P. volans were related to this decline. There was a marked difference in the distribution of resident adult P. volans at the two sites. Gliders at Wadbilliga had a relatively even distribution across the site and most of the site was permanently occupied. In contrast, gliders at Morton had an extremely clumped distribution. The majority of the site was unoccupied (forest type A) and resident animals were restricted to forest types B and C which appeared to be the only favourable habitats within the site. The population density of P. volans did not appear to be related to forest site productivity. Based on the entire area of the site, the number of resident adult P. volans per hectare was 0.18 at Morton; but on the basis of the area of forest apparently suitable for occupation the population density of gliders was 0.89 animals ha-l in forest type B and 1.67 animals ha-l in forest type C. This was then higher than the population density of P. volans at Wadbilliga (0.88 animals ha-l). In contrast, the annual fecundity of the populations of P. volans was related to forest site productivity. Resident animals at Wadbilliga and Morton forest type C successfully raised young during each year of the study but those in Morton forest type B did not, although their social cycle was comparable to gliders elsewhere. Neither Wadbilliga nor Morton appeared to have experienced major disturbances such as wildfire in recent years, and neither predation nor the availability of den sites appeared to influence the distribution of resident gliders. The majority of data on the behaviour and feeding ecology of P. volans were consistent with the following observations. The observed distribution and fecundity of P. volans in each forest appeared to be related to the availability of high-quality food and this factor was an important determinant of habitat quality. At Morton, for example, the amount of such foods in forest type A was considered to be insufficient to support resident P. volans. Although high-quality food was available in forest type B, the amount of this food, at least during the study, was insufficient for successful production of offspring by resident P. volans. The foraging behaviour of P. volans at both sites differed little. All gliders attempted to maintain a high intake of new leaf growth in their diet in all seasons so foraging was closely related to the spatial and temporal availability of this food. Female P. volans at Wadbilliga and Morton forest type C, for example, spent less time foraging and were able to meet the majority of their annual food requirements from a smaller area of forest compared to females in Morton forest type B. As a consequence, females at Wadbilliga and Morton forest type C also probably expended less energy foraging compared to those in Morton forest type B. These data, combined with those on forest site productivity and eucalypt phenologies, were consistent with the hypothesis that the availability of high-quality food was higher at Wadbilliga and Morton forest type C compared to that at Morton forest type B and particularly Morton forest type A. P. volans consistently foraged for and browsed eucalypt foliage that was high in nitrogen concentration. However, my data were insufficient to implicate foliar nitrogen as the ultimate factor determining browse selection by this species. Clearly, many other foliar constituents, either independent of or in association with nitrogen, may be implicated in browse selection and influence the dietary quality of foliage for P. volans. New data on aspects of the ecology of P. volans that are relevant to its management are presented. A polygyny threshold model that may account for all of the known data on the distribution, population fecundity and mating associations (i.e. monogamy or facultative monogamy) exhibited by P. volans throughout its range is given. Application of this model may have considerable potential for identifying the high-quality habitat required by P. volans. Finally, areas warranting further research are outlined
gliders, Petauroides volans, forest ecology, eucalypt forest, habitat
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