Comparison of bobuck (Trichosurus cunninghami) demography in two habitat types in the Strathbogie Ranges, Australia


Jennifer K. Martin, Department of Zoology, The University of Melbourne, Vic. 3010, Australia.


The demographic characteristics of populations are determined by the life-history strategies of their constituent individuals. Habitat characteristics, such as the availability of key resources, shape life-history strategies; thus habitat variation may result in intraspecific variability in demography. We studied two neighbouring populations of bobucks or mountain brushtail possums Trichosurus cunninghami within a fragmented forest system. One population occurred in a forest patch that was selectively logged in the last 40 years; the other occupied narrow strips of linear roadside remnant vegetation that have not been logged for at least 100 years. Many demographic parameters of the two populations were similar, and were consistent with those described previously for a bobuck population living in continuous forest. For example, both sexes were long-lived (at least 12 years), but there were fewer males in the oldest age classes at both sites. Most females produced one young per year and reproduction was highly seasonal. Females in the oldest age classes produced young, but none of these survived to pouch emergence. There were also marked differences between our two study populations: the sex ratio of adults was equal at the forest site but female-biased (1.7:1) at the roadside site. Forest males weighed significantly less than males at the roadside site and females at both sites. The peak of births occurred more than a month later at the roadside than at the forest site. The sex ratio of roadside offspring did not differ significantly from parity; however, the sex ratio of young at the forest site was significantly male-biased (62% of young). This demographic variation may be explained by differences in habitat characteristics (particularly logging history); a detailed investigation of resource availability at the two sites is warranted. Our results highlight the importance of studying multiple populations when attempting to describe the population ecology of a species.