Abstract
Australia’s native marsupial fauna has just two primarily flesh-eating ‘hypercarnivores’, the Tasmanian devil (Sarcophilus harrisii) and the spotted-tailed quoll (Dasyurus maculatus) which coexist only on the island of Tasmania. Devil populations are currently declining due to a fatal transmissible cancer. Our aim was to analyse the diet of both species across their range in Tasmania, as a basis for understanding how devil decline might affect the abundance and distribution of quolls through release from competition. We used faecal analysis to describe diets of one or both species at 13 sites across Tasmania. We compared diet composition and breadth between the two species, and tested for geographic patterns in diets related to rainfall and devil population decline. Dietary items were classified into 6 broad categories: large mammals (≥ 7.0kg), medium-sized mammals (0.5–6.9kg), small mammals (< 0.5kg), birds, reptiles and invertebrates. Diet overlap based on prey-size category was high. Quoll diets were broader than devils at all but one site. Devils consumed more large and medium-sized mammals and quolls more small mammals, reptiles and invertebrates. Medium-sized mammals (mainly Tasmanian pademelon Thylogale billardierii), followed by large mammals (mainly Bennett’s wallaby Macropus rufogriseus) and birds, were the most important prey groups for both species. Diet composition varied across sites, suggesting that both species are flexible and opportunistic foragers, but was not related to rainfall for devils. Quolls included more large mammals but fewer small mammals and invertebrates in their diet in the eastern drier parts of Tasmania where devils have declined. This suggests that a competitive release of quolls may have occurred and the substantial decline of devils has provided more food in the large-mammal category for quolls, perhaps as increased scavenging opportunities. The high diet overlap suggests that if resources become limited in areas of high devil density, interspecific competition could occur.
Highlights
Co-existence of mammalian carnivores involves complex interspecific interactions and trophic dynamics [1, 2]
We aim to address the following specific questions: (1) what is the relative importance of the prey species consumed by devils and quolls across their sympatric range? (2) what is the diet breadth and diet overlap of these two carnivores and how can it help to understand resource partitioning patterns? (3) is there partitioning in prey-size and/or vertical niche that could minimise competition? and (4) has the population decline of Tasmanian devils from DFTD affected the diet of quolls?
We collected 660 Tasmanian devil scats from 10 sites and 177 spotted-tailed quoll scats from 7 sites (Table 1)
Summary
Co-existence of mammalian carnivores involves complex interspecific interactions and trophic dynamics [1, 2]. Carnivore diets are influenced by the diversity, abundance and availability of prey resources, which may vary in space or time, as well as by competitive interactions with sympatric carnivore species. High dietary overlap between sympatric carnivores may indicate resource competition [10, 13,14,15]. This can lead to aggressive encounters and intraguild predation because carnivores searching for the same prey item are more likely to encounter one another [16, 17]. Determining the degree of dietary overlap is a useful first step in investigating whether resource competition might exist between sympatric carnivores
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