Herbivory of common brushtail possum (Trichosurus Vulpecula, Marsupialia: Phalangeridae) at different scales of resource heterogeneity.

Karolina Petrovic

    Research output: ThesisDoctoral Thesis

    591 Downloads (Pure)

    Abstract

    Resource heterogeneity has been a broadly discussed concept in ecology used to explain adaptive responses of herbivores to the distribution, abundance, and nutritional quality of forage, as well as the patchy distribution of other key resources (i.e., shelter) and interactions with competitors and predators. However, few studies have considered that generalist herbivores exhibit resource selectivity at different scales of environmental heterogeneity. Australian arboreal marsupials represent a unique opportunity for exploring herbivore nutrition as they represent a continuum from specialist to generalist herbivores, live in habitats dominated by a single tree genus (Eucalyptus) of varying nutritional quality, and rely on trees as a shelter and platform for facilitating interactions with conspecifics, competitors, and predators.In this study, resource selectivity of a generalist arboreal marsupial, the common brushtail possum (Trichosurus vulpecula, Marsupialia: Phalangeridae), was examined in the context of forage availability and nutritional quality at three different scales, landscape, home range, and individual tree, with tree-dependant parasitic plants representing a special case of small-scale resource heterogeneity. Furthermore, other factors associated with tree use by common brushtail possums were explored, including availability of shelter (tree hollows) and presence of competitors, the mountain brushtail possum (Trichosurus cunninghami). Integrative field and laboratory techniques were employed, including spotlighting, radio-tracking, and faecal content analysis. The chemical variability of trees and parasitic plants was studied using a recently developed method for estimating the nutritional quality of forage for herbivores or foliar concentrations of available nitrogen.The present study has demonstrated that common brushtail possums had a broad diet, including the most common, but chemically defended and hard-to-digest Eucalyptus species; nitrogen-rich Acacia species; succulent parasitic plants, drooping mistletoe (Amyema pendula) and cherry ballart (Exocarpos cupressiformis); and supplemented their diet with other plant groups. However, animals were selective over multiple scales of resource heterogeneity, ranging from across a landscape to individual home ranges to specific species of trees, individual trees, and discrete patches of mistletoes within tree canopies. They preferred parasitic plants over their tree hosts and selectively foraged on trees parasitized by mistletoes. They used Eucalyptus species less than expected from their availability in the habitat, and were found foraging on both Monocalyptus and Symphyomyrtus species of differing nutritional quality. Moreover, tree choices and space-use patterns of common brushtail possum were shaped by the availability of hollows and the presence of mountain brushtail possums.The current research has shown that studying herbivory over different spatial scales, landscape, home range, and individual plants, allows general conclusions to be made about the nature of herbivore nutrition, focusing not only on food availability and nutritional quality, but also on a broader context of ecological interactions with conspecifics and competitors. Moreover, this study has shown that focusing on a single measure of the nutritional quality of forage for herbivores, available nitrogen, simplifies complex interactions between multiple nutrients and herbivore-deterrents. Therefore, future studies should encourage a more holistic approach when analysing availability and nutritional quality of forage for herbivores.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    Supervisors/Advisors
    • Watson, David, Co-Supervisor
    • Lunt, Ian, Co-Supervisor
    Award date01 Sep 2014
    Place of PublicationAustralia
    Publisher
    Publication statusPublished - 2014

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