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Links between ontogeny, chemical and physical characteristics of foliage and mammalian herbivory in Eucalyptus nitens
thesisposted on 2023-05-26, 18:34 authored by Loney, Prue Elizabeth
Throughout plant development from seeds to seedlings, juveniles and mature stages a plant's palatability or resistance to herbivory is likely to change. Such ontogenetic changes can be due to changes in chemical and physical characteristics of the foliage. Consequently, herbivores often prefer to feed on particular plant ontogenetic stages. The research presented in this thesis focuses on the effects of plant ontogeny on chemical and physical characteristics of Eucalyptus nitens foliage, and flow on effects for mammalian herbivory by the common brushtail possum (Trichosurus vulpecula), and the red-bellied pademelon (Thylogale billardierii). My research demonstrates that large changes in foliage chemical and/or physical characteristics occur during the early seedling stage, between young and old leaves within seedlings, and between juvenile and adult leaves within 4-year-old trees. Furthermore, evidence from feeding trials implies that these changes are likely to be associated with changes in mammalian herbivory. No single chemical or physical characteristic of the foliage could explain the patterns of herbivory observed across the onto genetic stages studied. In fact, certain chemical or physical characteristics affected foliage resistance to mammalian herbivores at some ontogenetic stages but not at others. Furthermore, the importance of particular chemical and physical characteristics differed between brushtail possums and pademelons, and under the types of conditions they were offered the foliage (i.e. no-choice and choice trials). Chemical analyses suggested that newly emerged seedlings become more protected from mammalian herbivores as they increased in age, with chemicals known to deter these herbivores (sideroxylonals and cineole) being present in minute quantities at seedling emergence. Within seedlings, pademelons preferred older leaves that contained the lowest concentration of sideroxylonals and cineole, while possums generally preferred young leaves high in sideroxylonals and cineole, but also high in nitrogen. Under choice conditions possums preferred juvenile over adult tree foliage, while under no-choice conditions they consumed as much adult foliage as juvenile. These results suggested that difference in leaf toughness affected feeding preference under choice condition but not under no-choice conditions. Currently ecological and evolutionary theories regarding interactions between plants and herbivores are largely based on studies conducted at a single ontogenetic stage. However, the large effects of ontogeny on the chemical and/or physical characteristics of the foliage and its palatability to herbivores shown in this thesis emphasise Boege and Marquis' (2005) assertion that the role of ontogeny should be an important component in plant defence theories.
Rights statementCopyright 2007 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references