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Abstract

In marine ecosystems, identifying what and where animals eat are inferred
through indirect methods. These methods are often inadequate and our ability to
measure and predict ecological interactions remains poor. The accuracy of diet
estimation in marine animals may be improved by the use of DNA based techniques,
a potentially valuable but largely untested approach. The predictive power of
ecological models may also be improved by synoptic integration of diet with
spatially explicit foraging activity. A further gain may be achieved by considering
individual variation in foraging behaviour, as reflected by differences in diet and
core foraging areas within a population.
The objective of this thesis was to investigate the utility of DNA based diet
analysis in foraging ecology, explored in the context of top marine generalist
predators, southern hemisphere fur seals (Arctocephalus spp.). The effectiveness of
DNA based diet analysis for identifying trophic relationships is assessed in a series
of captive and field based studies. The diet and foraging activity of individuals in a
free-living population are then matched both spatially and temporally, and
predator-habitat relationships are modelled with reference to specific predator-prey
combinations.
The accuracy of DNA based scat analysis for diet estimation was assessed in
Arctocephalus seals fed mixed prey diets integrated over several days. This approach
was compared with the most commonly used method, morphological scat analysis.
Both methods inferred recent diet (within 40 hours), but detection of robust prey
consumed was 1.4-5.8 times more likely using genetic analysis than morphological
analysis. Presence/absence data was an ineffective quantitative measure of diet
using either DNA or morphological methods.
Faecal samples from 54 wild lactating Arctocephalus gazella were analysed for
prey remains using both DNA and morphological techniques. Morphological
analysis implied that nearly all individuals (91%) consumed a monotypic diet, but
inclusion of molecular data showed that a large proportion (46%) of seals consumed
a more diverse diet DNA based diet analysis identified important predator-prey
relationships that were not revealed by morphological analysis.
Differences in diet between individuals were mirrored by foraging location
data, confirming individual differences in foraging behaviour. Persistent
environmental features were significant in describing and predicting core foraging
areas, irrespective of diet, suggesting that these areas are likely to be important
sources of prey in most years. Monotypic consumers may be more vulnerable in
years of poor prey availability. DNA based diet analysis provides a significant
contribution to our ability to understand foraging ecology.

Item Type:	Thesis - PhD
Authors/Creators:	Casper, Ruth Mariana
Copyright Holders:	The Author
Copyright Information:	Copyright 2008 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).
Additional Information:	Thesis (PhD)--University of Tasmania, 2008. Includes bibliographical references
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