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Niche overlap between Spotted-tailed Quolls and eutherian predators: evidence for competition?

Al Glen, Department of Environment and Conservation (NSW)

Email: al.glen@environment.nsw.gov.au

Abstract

A number of factors are thought to have caused the decline of the Spotted-tailed Quoll since European settlement in Australia, the destruction of habitat being the most significant. However, the impacts of introduced predators are also likely to have contributed. Quolls, foxes and feral cats occupy a similar dietary niche, and interspecific aggression may also occur. Similarly, wild dogs have the potential to compete with quolls, but may also suppress cats and foxes (Glen and Dickman 2005).

I examined overlap in resource use (dietary and spatial) of Spotted-tailed Quolls and eutherian carnivores in Marengo and Chaelundi state forests, north-eastern New South Wales. I also investigated mechanisms of niche partitioning, evidence for interspecific aggression, and possible effects of competition on the viability of quoll populations.

Analysis of scats from quolls, foxes and wild dogs revealed extensive dietary overlap, indicating potential for exploitation competition. Medium-sized mammals were the most important prey for all three predators, and indices of dietary overlap were high compared to carnivore guilds from Africa and South America. However, quolls consumed significantly more arboreal prey than their counterparts (Glen 2005; Glen and Dickman 2006a). This vertical dietary partitioning, and different size classes of secondary prey, may facilitate coexistence. Remains of D. maculatus were found in two dog scats, and cat hair in another, possibly indicating intraguild predation (Glen 2005).

Radio telemetry revealed extensive spatial overlap between quolls, foxes and feral cats. Thus, the presence of eutherian predators does not necessarily exclude quolls from an area. However, it is possible that avoidance occurs at a fine spatial scale, or that direct encounters are avoided by temporal separation. Spool-and-line tracking over a cumulative distance of 10,140 metres showed that, despite their consumption of arboreal prey, quolls made little use (1%) of standing trees (Glen 2005; Glen and Dickman 2006b). This suggests that habitat is unlikely to be divided vertically between quolls and eutherian predators. However, the climbing ability of quolls may provide a means of escape in direct encounters.

Population viability analysis showed that quoll populations may be vulnerable to extinction if subjected to high densities of competitors. Modelled reductions in carrying capacity (simulating exploitation competition) and increases in mortality (simulating interspecific killing) caused precipitous declines in the population's probability of survival (Glen 2005). Predator removal experiments are required to further clarify the relationships between Australia's mammalian carnivores and will be critical to guide informed management.

References

Glen, A. S. (2005). Ecology of the spotted-tailed quoll (Dasyurus maculatus), and its interactions with eutherian predators. PhD Thesis. University of Sydney, Sydney.

Glen, A. S. and Dickman, C. R. (2005). Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management. Biological Reviews 80, 387-401.

Glen, A. S. and Dickman, C. R. (2006a). Diet of the spotted-tailed quoll (Dasyurus maculatus) in eastern Australia: effects of season, sex and size. Journal of Zoology (London) 269, 241-248.

Glen, A. S. and Dickman, C. R. (2006b). Home range, denning behaviour and microhabitat use of the carnivorous marsupial Dasyurus maculatus in eastern Australia. Journal of Zoology (London) 268, 347-354.

Page last updated: 27 February 2011