| 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. 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". |
.
| 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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|
Two thylacines at the
Beaumaris Zoo (SB), circa 1911-1915, one of which is a male caught at Tyenna
in August 1911 by bushman Bill Power.
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