Marsupial carnivore feeding ecology and habitat use

Decline and loss of Australia’s marsupial carnivores

At the time of European settlement, Tasmania’s marsupial carnivore guild consisted of the thylacine and three dasyurids: the Tasmanian devil, spotted-tailed quoll and eastern quoll. Thylacines were distributed throughout the island, apart from the southwest. Their numbers were thought to have declined rapidly after 1905, though reports as far back as the 1850′s suggest the population was in decline. Despite the thylacine’s obvious decrease in abundance, the species did not receive official protection from the Tasmanian government until two months before the last known captive animal died in 1936.

Other marsupial carnivores face extinction threats. The Tasmanian devil experienced dramatic population declines in the 1850′s, 1920’s and late 1990’s. The most recent collapse in Tasmanian devil numbers has been attributed to a fatal contagious cancer that has spread across their range. The last known mainland population of eastern quolls were sighted in the 1960′s and are believed to be extinct. The range of Eastern quolls has reduced by 50-90% since European colonisation and currently has a widespread but patchy distribution in Tasmania. A few small pockets of spotted-tailed quolls are present in high rainforest areas of Victoria and northern Queensland. The decline of quoll species is slower in Tasmania due to the absence of red foxes until recently in the region. Understanding the ecology of the thylacine and driving forces behind their extinction may aid in the management of remaining marsupial carnivores that are in danger of extinction.

Research Aim

The primary aim of my PhD research is to better understand the feeding ecology of one of Australia’s largest marsupial carnivores, the thylacine and the factors that drove it to extinction – as there are currently many conflicting interpretations. Much of our understanding of their feeding and predatory behaviour comes from anecdotal accounts, which may not fully represent the behaviour of the species.

Marie Attard investigating the diet and predatory behaviour of the extinct thylacine, or Tasmanian tiger using stable isotopes and skull biomechanics.

How can we tell what they did, or didn’t eat nearly 80 years since the last known thylacine died?

The diet and foraging behaviour of the Tasmanian tiger remains a highly controversial subject due to contradictory anecdotal accounts and unusual morphological features. Based on their dentition, it is almost certain that they were hyper-carnivores, with a diet consisting of vertebrate flesh.

I used two novel techniques commonly used in paleoecology and ecological studies to:

  1. Determine whether diet specialisation and competition influenced the extinction of the thylacine, and
  2. Explore long-term shifts in marsupial carnivore diet and habitat use to test their resilience to environmental change.

I used state of the art 3D computer simulations of a thylacine skull to determine how effective their skulls were in capturing and killing prey compared to extant carnivorous marsupials. By comparing their diet to related living species with known feeding behaviour, I will be able to determine whether they were capable of taking down large prey.

In addition, I measured stable isotope ratios of carbon and nitrogen in museum preserved thylacines to investigate diet variation between and within individuals. Long-term trends in the ecology of the Tasmanian devil, spotted-tailed quoll, eastern quoll and thylacine were investigated by comparing stable isotope signatures of tissues collected from the 1830′s to present.

Research Findings

1. Limitation in prey size? Past comparative morphology studies on the thylacine suggest a potential limitation in the size of prey consumed, and our biomechanics findings support a preference towards small prey. Recent work on mammalian carnivore energetics suggests that the thylacine may have been particularly vulnerable if it was limited to eating small prey. With this inherent vulnerability, thylacines may have been less well adapted to cope with environmental disturbances such as intensive hunting and habitat degradation following European arrival.

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Podcast: The Science Show Radio with Marie Attard speaking about her research on thylacine feeding ecology and extinction risk.

2. Prey composition Stable isotope ratios of the thylacine and potential prey species were successfully used to assess the contribution of different prey types to the diet of this predator. I am currently preparing the manuscript for publication – so stay tuned!

3. Long-term shifts in marsupial carnivore ecology Temporal changes in the behaviour of top predators presents an important consideration for species conservation and management. I assessed temporal changes in the stable isotope values of thylacines and living marsupial carnivores in Tasmania using tissue samples collected from specimens dating from the 1830′s to now.

Our findings reveal fluctuations in the stable isotope ratios of carbon and nitrogen in extant marsupial carnivore species over the past 180 years. My collaborators and I are currently teasing apart the data to determine the most likely cause for the trends observed – which may include shifts in carnivore habitat use and diet or changes in nutrient inputs and/or vegetation composition.

Affiliations

My PhD research to assess the ecology of Australia’s largest marsupial carnivores would not be possible without the generous assistance of museums, curators, organisations and colleagues that have contributed to the research.

Museums

Tissue samples have also been generously provided by Miss Bronwyn Fancourt at the University of Tasmania, Sarah Peck at the Department of Primary Industries, Parks, Water and Environment (DPIPWE) and Damien Stanioch.

Photo: Tammy Gordon (Curatorial officer) and Marie Attard at QVMAG with a string of Eastern quoll skins to sample.

Captive Study

The Australian Reptile ParkAustralia Walkabout Wildlife ParkDreamworldKyabram Fauna ParkTaronga Conservation Society Australia and Taronga Western Plains Zoo participated in the captive Tasmanian devil study. We are grateful to Nick de Vos, Anthony Britt-Lewis, Todd Jenkinson, Fiona Cameron, Nana Satake, Kerry Fanson, Tamara Keeley, Ron Pope, Kezia Talbot, Nick Carson, Jill Perry, Liz Vella, Brad Gabriel and Sophia Essex and husbandry staff for their assistance in conducting the Tasmanian devil whisker growth rate trials at each institution.

We acknowledge the STDP, ZAA and DPIPWE for permitting the use of captive Tasmanian devils from the Insurance Population.

Volunteers

Thank you to my field assistant, Christopher Hammang who has been an invaluable member of this research effort.