A study of stable carbon, nitrogen and oxygen isotopes in modern Australian marsupial herbivores, and their relationships with environmental conditions
Abstract
This research has examined the stable isotope ecology of three species of Australian marsupial
herbivores; koalas, kangaroos and wombats, from a range of different geographic and climatic
regions. The broad objective of this thesis research was to examine stable isotopes in modem
marsupial species to provide baseline data that can be used to inform palaeoecological studies.
In the European, African and north American continents stable isotope analyses of terrestrial
mammal remains are widely used to investigate the diet and ecology of modern and fossil
species. By comparison, similar investigations using Australian native mammals are not as
prevalent. Australian landscapes and the physiologies of some native marsupials are in many
respects almost unique; therefore, an isotopic study of this continent is warranted. The
investigation of modern specimens provided the experimental conditions to observe some of the
baseline systematics of stable isotopes in marsupial tissues.
Firstly, the study explored the relationships between stable isotopes in the animals' diet, bone
collagen and dental enamel, and the isotopic differences between these two tissues. Secondly, it
examined isotopic variability on different levels: intra-population variability in o13C and o15N
values in bone collagen and both inter and intra-tooth variability in o13C and o180 values in
enamel. Thirdly, it examined the relationships between marsupial stable isotope ratios and
environmental signals such as moisture availability, rainfall and habitat.
The koalas provided an opportunity to examine an obligate C3 browser with an extremely
consistent diet and conservative lifestyle. The constant nature of their diet enabled the effects of
climate on stable isotope ratios to be examined with the knowledge that there is no C4 dietary
input. The stable isotopes in the kangaroos and the wombats were examined from a broader
environmental perspective than the koalas because their geographic coverage is far more
extensive- from the arid to the alpine. Because the kangaroos and wombats are both grazers,
their o13C values reflected the availability of the C3 and the C4 plants in their respective habitats.
Most significantly, microsampling of the continuously growing incisors of wombats revealed
that variation in 813C and 8180 values along the tooth can be used as a proxy for seasonality.
The results from this research provide empirical data for future research in isotopic
biochemistry and significant baseline data for use in palaeodietary modelling and
palaeoenvironmental interpretation of fossil marsupials. These findings are specific to the
Australian palaeoecological context.