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Vulnerability of a focal plant to browsing by generalist mammalian herbivores : relative importance of self and neighbours


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Miller, Alison May 2006 , 'Vulnerability of a focal plant to browsing by generalist mammalian herbivores : relative importance of self and neighbours', PhD thesis, University of Tasmania.

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In a heterogeneous environment, where food occurs as patches, herbivores have the
opportunity to select at many scales, including vegetation patches, and individual
plants within patches. The probability that a focal plant will be browsed may
therefore depend not only upon its own physical and chemical characteristics, but
also on those of the surrounding vegetation. Consumption of focal plants has been
related to their own characteristics and to the quality of the neighbouring
vegetation, but the relative importance of the two has received little attention, and
as such, forms the focus of this thesis.
I used a combination of captive animal and field trials to examine the relative
importance of characteristics of a focal plant and the surrounding vegetation to
browsing of the former by generalist mammalian herbivores (primarily the red
bellied pademelon, Thylogale billardierii). This involved manipulating the
palatability of focal plants, in this case Eucalyptus seedlings, by either fertilising or
applying a chemical repellent. Consumption of seedlings was then examined, over
a series of trials, in vegetation patches of varying height, palatability and density,
and where herbivores had either a choice or no choice of vegetation patches.
Results were considered in light of various hypotheses predicting plant
vulnerability, including the associational plant refuge, short-term apparent
competition, and apparency hypotheses.
I found that both focal seedling and patch characteristics were important factors
influencing browsing of seedlings. Seedlings of higher palatability were browsed
more than those of low palatability. The relative quality, abundance and height of neighbouring vegetation all influenced browsing of seedlings through their
influence on apparency, availability and relative palatability to herbivores. The
influence of the surrounding vegetation depended on the scale at which herbivores
were able to, or chose to, make foraging decisions. Seedling and vegetation effects
were often additive. Many behaviours exhibited in captive animal trials were
tested and confirmed in the field.
Results demonstrate that animals can select at both the patch scale and at the scale
of individual plants within patches. They demonstrate the need to consider
characteristics of both the focal plant and its neighbouring vegetation when
predicting the vulnerability of the former to browsing by generalist herbivores.
Although I tested a number of hypotheses about plant vulnerability, most of these
could be predicted from the same general foraging theory, i.e. herbivores maximise
foraging efficiency based on available choices. As such, I demonstrate how many
of these hypotheses can be combined into a broader, more general foraging model.
In addition to the fundamental importance of these results, they have applications
to the forestry industry. Tree seedlings growing in forestry plantations are often
damaged by mammalian herbivores during the early stages of establishment. This
damage can reduce plantation productivity and, as such, is typically controlled
using lethal methods to reduce herbivore populations. Results show that both
seedling quality and vegetation on plantations can be manipulated to reduce
browsing of tree seedlings. Seedling and vegetation management therefore has the
potential to reduce reliance on lethal methods for managing browsing in

Item Type: Thesis - PhD
Authors/Creators:Miller, Alison May
Keywords: Animal-plant relationships, Herbivores, Herbivores, Pademelons
Copyright Holders: The Author
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Copyright 2006 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
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Additional Information:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2006. Includes bibliographical references. Ch. 1. General introduction -- Ch. 2. Preferences of two mammalian herbivores for tree seedlings and potential cover crops in plantation forestry -- Ch. 3. Alkaloids of two Lupinus species: variation in allocation with respect to plant part and growth stage -- Ch. 4. Effects of within-patch characteristics on the vulnerability of a plant to herbivory -- Ch. 5. Characteristics influencing browsing of focal plants under conditions of patch choice by a generalist mammalian herbivore -- Ch. 6. Characteristics of tree seedlings and neighbouring vegetation have an additive influence on browsing by generalist herbivores -- Ch. 7. Effects of tree seedlings and cover crop characteristics on seedling growth and defoliation by insect and mammalian herbivores -- Ch. 8. General Discussion

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