Metapopulation Viability of Arboreal Marsupials in Fragmented Old‐Growth Forests: Comparison Among Species

Abstract

Computer simulation analyses using a generic package for population viability analysis (PVA) were used to examine the dynamics of a limited number of metapopulation structures of the mountain brushtail possum, Trichosurus caninus, and the greater glider, Petauroides volans. These arboreal marsupials inhabit tall eucalypt forests in southeastern Australia. As in a parallel study of Leadbeater's possum, Gymnobelideus leadbeateri, the results indicated that there are some metapopulation structures in which increased movement between habitat patches may have a detrimental effect on demographic stability and, in turn, reduce population persistence. These negative impacts were most pronounced in model metapopulations composed of an ensemble of very small subpopulations of 4, 10, or 20 animals. The patterns were accentuated with increased inter‐patch movement as well as the addition of further small subpopulations. These counter‐intuitive findings appear to result when animals from already unstable and declining sub‐populations disperse into unoccupied patches of habitat that act as a type of population sink. These trends in population demography were reversed in scenarios in which larger subpopulations of 40 animals were modeled. In such cases the impacts of movement and additional habitat patches on subpopulation and metapopulation dynamics were positive. In contrast to the results for various demographic parameters, increased movement and added subpopulations had a beneficial effect on genetic variability among all the types of metapopulation structures that were examined. Results for the two species were compared to each other and also with investigations of Leadbeater's possum, Gymnobelideus leadbeateri. These comparisons confirmed general trends but also revealed potential quantitative differences in the behavior of metapopulations of T. caninus, P. volans, and G. leadbeateri. Many of these differences were attributed to variations in key life history parameters such as birth and death rates, but trends in metapopulation viability did not correlate simply with intrinsic rates of population growth. The three species differed in the size of metapopulations required for demographic and genetic stability, and the rank order of their susceptibility to demographic and genetic stochasticity may not be consistent. Different species, even those within the same guild, may vary in vulnerability to disturbance and environmental perturbation. Our analyses also emphasized the need to understand the structure and composition of metapopulations in the development of strategies for conservation of wildlife at the landscape and regional scales.