The risks of being big - The ecological and evolutionary significance of the thylacine’s body size and diet

Background/Question/Methods

Australia's iconic thylacine, Thylacinus cynocephalus, also known as the Tasmanian tiger, was the largest apex predator to survive up to modern times in Tasmania. After over a century of persecution by European settlers, the species became extinct in 1936. The status of the extinct thylacine as a meat specialist has been universally agreed upon, but whether they were a predator of relatively large mammalian prey remains a long-running subject of debate. We investigate maximum prey size and the degree of dietary specialization in the thylacine and its potential implications in their extinction. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) of tissues from thylacine and potential prey and a multiple-source mixing model (MixSIR) were used to assess the predominate prey types contributing to the diet of the population. Their degree of individual dietary and habitat specialization was investigated using sequentially sampled thylacine vibrissae.

Results/Conclusions

We inferred that hunting of medium to large bodied mammals was likely a major element of thylacine subsistence in Tasmania, and may have included Common wombats, Bennett's wallabies and Tasmanian pademelons. Individuals were highly specialized in their δ¹³C and δ¹⁵N values relative to the population. This may be attributed to the adoption of different feeding strategies, or alternatively, differences in prey abundance and distribution in time and space may give the appearance of individual specialization relative to the total niche space occupied by the population. Individual consistency in diet and habitat provides the advantage of reducing intraspecific competition and/or alter selective pressures, yet potential constraints in the ability of individuals to switch between resources. The dramatically reduced abundance and range of Tasmania's large mammalian herbivores following European settlement has important implications for the thylacine population that were heavily reliant on large-bodied prey. The high degree of niche overlap between sympatric marsupial carnivores may have lead to high competitive pressure for similar resources. Understanding extinction risk factors in the thylacine has provided valuable information for the conservation and preservation of Australia's last few remaining large marsupial carnivores that face similar challenges for their survival.