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BIOLOGY:
- BEHAVIOUR -
(page 8)
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Predation:

    Undoubtedly, the thylacine's main predator, as is the case with all of the large carnivores, was man.  There is evidence in a number of rock art paintings and within aboriginal folklore (Reynolds 1995) to suggest that Aboriginal peoples hunted the thylacine as a source of food.  It is believed (though not proven) that the dingo (Canis lupus dingo) may have attacked and killed thylacines, and therefore actively contributed to their mainland extinction.  The Tasmanian devil (Sarcophilus harrisii) and Wedge-tailed eagle (Aquila audax) were also reported to have killed and eaten the young of the thylacine (Bailey, pers. comm.).  Thylacine young were particularly vulnerable to predation whilst resting in the lair when their parents were out hunting.

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Aboriginal hunting party, circa 1930
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Aboriginal hunting party, circa 1930.  Unknown source.
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    In a recent paper (Letnic et al. 2012) entitled "Could Direct Killing by Larger Dingoes Have Caused the Extinction of the Thylacine from Mainland Australia?" researchers obtained comparative measurements of 21 dingo and 24 thylacine specimens from Holocene deposits in temperate southwest Australia and the semi-arid Nullarbor region of Western Australia.  They state: 

    "Based on the diameter of the limb bones, dingoes were on average heavier than thylacines, although there was considerable overlap in estimated body mass, and mass in both species tended to be lower in the arid Nullarbor regions.  These results support the hypothesis that dingoes would have been dominant in one-on-one agonistic encounters between the species owing to their larger body size.  Moreover, the dingo's size advantage over the thylacine may have been exacerbated by that fact that dingoes often live in packs that hunt cooperatively, while there is little evidence of thylacines doing the same.

    Sexual dimorphism was likely to have had major implications for the outcomes of interactions between dingoes and thylacines.  Based on body size alone, large thylacines may have been capable of matching a dingo in a direct confrontation.  Female thylacines would have been very vulnerable to being killed in direct one-on-one encounters with dingoes.  Killing of female thylacines by dingoes could conceivably have resulted in the extinction of thylacines if it depressed the reproductive output of the thylacine population so that their rate of mortality was above the rate of the recruitment.  Such a scenario does not seem implausible given that thylacines may have lacked adaptations to detect, avoid and escape invasive dingoes. 

    Examples of larger predators suppressing the abundance of smaller predators are many, and the effects of larger predators tend to be exacerbated when the predator is an invasive species.  Another mechanism through which larger predators can affect smaller predators adversely is through aggressive interference or encounter competition; here, small predators avoid larger species, and modify their behaviour to reduce the risk of encounters with larger predators.  Such competition can conceivably suppress the abundance of smaller predators if it results in their access to resources being severely curtailed, and might be expected to occur given the size difference between dingoes and female thylacines.

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    Previous authors have suggested that dingoes may have driven thylacines to extinction through competition for prey.  Metabolic rate in dasyurid marsupials is considerably lower than that of similar sized carnivores.  Thus, it is likely that on a percapita basis dingoes may have needed to consume a greater mass of prey than a thylacine of a similar size.  Moreover, when they first arrived in Australia, dingoes may have had a greater impact on prey populations than thylacines because they were a novel predator against which Australian prey had not evolved antipredator defences.  Hence, competition between the two species may have been considerable.  However, contemporary understanding of the processes of biological invasion and exploitative competition suggest that it is unlikely that competition with dingoes would have been the primary factor that caused the extinction of the thylacine.  This is because competition has rarely been identified as the primary driver of extinction events, and is thus considered a weak extinction threat". 
mother dingo (Canis lupus dingo) with pup
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A mother dingo (Canis lupus dingo) with pup.

    The research team reached the following conclusions: 

    "Dingoes were similarly sized to male thylacines but were considerably larger than female thylacines on mainland Australia during the Holocene.  Small size may have made female thylacines particularly susceptible to direct killing by dingoes and such killing could have driven thylacines to extinction.  Due to their lower metabolic rate and convergent morphology, thylacines would have also been susceptible to resource competition with dingoes, but competition is generally thought to be a weaker extinction threat than predation.  Our results provide support for the hypothesis that direct killing by larger dingoes contributed to the extinction of the thylacine on mainland Australia.  However, attributing the extinction of the thylacine to just one cause is problematic because the arrival of dingoes coincided with another potential extinction driver, the intensification of the human economy".

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References
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