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Guild structure of the large marsupial carnivores in Tasmania

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Jones, ME (1995) Guild structure of the large marsupial carnivores in Tasmania. PhD thesis, University of Tasmania.

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Abstract

The principal focus of community ecology is to detect patterns in natural
assemblages of plants and animals and explain the causal factors that underlie them.
For the last 30 years, much of ecological theory has assumed that competition is the
primary structuring force in communities. Competition is likely to be most important
at the lower levels of community organisation, that of the guild. At the scale of large
geographic regions, both evolutionary history and the physical environment are
important in determining the composition of species assemblages. The structure of
the guild of large dasyuroids or marsupial carnivores in Tasmania, Australia, is
examined in relation to causal factors, especially the importance of competition. The
relative significance of evolutionary history and the physical environment in shaping
the composition of the Australian marsupial carnivore fauna is assessed.
Evidence that competition was and still is an important structuring force in the
guild is found. Evolutionary evidence is found in character displacement and
morphological size patterning in canine strength, the trophic structure proximally
related to feeding ecology of the large dasyuroids. The hypothesis of competition as
the underlying causal factor is supported by similar patterning in prey size and a
carnivore body size / prey size correlation. The existence of current competition in
the guild can be inferred from the large extent of dietary overlap between species.
The effects of competition are most evident between the two most similar species,
the congeneric quolls. Resources are partitioned on at least three niche dimensions,
diet, horizontal and vertical use of the habitat. Where dietary overlap is high between
species, habitat use overlap is low, thereby reducing the potential for direct
competition for individual prey items. Interference competition is most likely to
occur over large carcasses. Mainly body size but also age of the carnivore determine
interspecific dominance. Devils are usually dominant and are the primary scavengers,
exhibiting adaptations for scavenging that are lacking in the other two species.
Aspects of guild structure are influenced by several factors as follows. Size
relationships in both body size and trophic stuctures are influenced by - latitudinal
size correlations, competitive character displacement, size distributions of prey
species which are shaped by the fractal dimensions of the habitat, and sexual
selection. Locomotor morphology and habitat use of the carnivore species show
evolutionary adaptations that match the arboreal or terrestrial habits of their
particular size range of prey species. Competition may result in the depression of
species populations. The rarity of spotted-tailed quolls can possibly be explained by
higher dietary overlap and competition than is experienced by the other species.
Numerical dominance of the guild by devils may relate in part to large body size and
behavioural dominance in feeding situations.
Substantial ecological convergence has occurred between the marsupial carnivore
fauna of Australia and eutherian carnivore faunas on other continents. The main
differences are the low diversity of species and eco-morphological types in Australia,
which relate to poor soils and aridity. This supports the general view that the physical
environment is more important than evolutionary history in shaping the composition
of faunal assemblages.

Item Type: Thesis (PhD)
Keywords: predator interactions, carnivore guild, competition, Tasmanian devil, thylacine quoll
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Date Deposited: 18 Jul 2011 02:19
Last Modified: 11 Mar 2016 05:55
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