University of Tasmania, Australia

Predators are essential components of healthy ecosystems, and top predators especially are often keystone species responsible for sustaining biodiversity and ecosystem function. Large predators suppress the abundance and behaviour of mesopredators that might otherwise become over-abundant and threaten susceptible prey species; they also control populations of herbivores and thus help to prevent degradation of habitat through excessive herbivory. Top predators are not only important in maintaing the structure of native ecosystems, they can also control the impact of invasive species. We are studying the interactions of top predators, native and invasive mesopredators and prey species in Tasmania and the far north of Australia (Arnhem Land and the Kimberley). The Tasmanian projects focus on the ecosystem consequences of decline of the Tasmanian devil. The northern Australian projects are investigating the causes of decline of small mammals throughout the tropical savannas, and especially are aimed understanding the role of feral cats in driving these declines.

The Tasmanian devil population is in steep decline because of high mortaility caused by Devil Facial Tumor Disease (DFTD), which continues to spread across the State and has caused population declines of more than 90% in affected areas. Devils are the largest predators in the Tasmania ecosystem, and they have strong interactions with two species of quoll and the invasive feral cat, as well as with a variety of prey species (pademelons, possums etc). We are monitoring changes in the abundance of these other species as devils decline, using behavioural experiments and predator-prey models to understand the mechanims that cause these changes, and focussing on changes in key species including the eastern quoll (which is currently declining) and feral cats (which may be increasing). These projects are closely related to past and continuing work on the nature and impacts of DFTD, and involve close collaboration with the State Government Save the Tasmanian Devil Program with the aim of finding ways to prevent extinction of the devil in the wild and reduce the ecological effects of devil decline.

Small mammals are curently declining trhoughout the tropical savannas of northern Australia. We are collaborating with the Australian Wildlife Conservancy and other researchers in northern Australia to discover the cause of these declines. In the Kimberley, we are studying the behavioural ecology of feral cats to understand how their impact on small mammals is affected by landscape, fire and livestock grazing, and we are also testing the role of dingoes in reducing cat impact on their prey. In Arnhem Land we are running a landscape-scale experiment which is excluding cats from large patches of savanna woodland to test the effect of cat predation on population growth of reintroduced small mammals and community structure of reptiles. These studies aim to produce ecologically-based management strategies that will maintain small mammal diversity in the northern savannas.

(selected publications)

Woinarski, J. C. Z., Legge, S., Fitzsimons, J. A., Traill, B. J., Burbidge, A. A., A. Fisher, A., Firth, R. S. C., Gordon, I. J., Griffiths, A. D., Johnson C. N., McKenzie, N. L., Palmer, C., Radford, I., Rankmore^, B., Ritchie, E., Ward^, S. & Ziembicki, M. (2011) The disappearing mammal fauna of northern Australia: context, cause and response. Conservation Letters 4, 192-201

Wallach, A., Johnson, C. N., Ritchie, E. G. & O’Neill, A. J. (2010) Predator control promotes invasive-dominated ecological states. Ecology Letters 13, 1008-1018

Hamede R. K., Bashford J., McCallum H., & Jones, M. (2009) Contact networks in a wild Tasmanian devil (Sarcophilus harrisii) population: using social network analysis to reveal seasonal variability in social behaviour and its implications for transmission of devil facial tumour disease. Ecology Letters, 12 (11), pgs. 1147-1157

Jones, M.E., Cockburn, A., Hawkins, C., Hesterman, H., Lachish, S., Mann, D., McCallum, H., Pemberton, D. (2008) Life history change in disease-ravaged Tasmanian devil populations. Proceedings of the National Academy of Science, 205, pgs. 10023 - 10027

Ritchie, E. G. & Johnson, C. N. (2009) Predator interactions, mesopredator release and biodiversity conservation. Ecology Letters 12, 982-998

Jones, M. E., Jarman, P. J., Lees, C. M., Hesterman, H., Hamede, R. K., Mooney, N. J., Mann, D., Pukk, C. E., Bergfeld, J. & McCallum, H. I., (2007) Conservation management of Tasmanian devils in the context of an emerging, extinction-threatening disease: Devil Facial Tumor Disease.  EcoHealth, 4, 1612-9202

Johnson, C. N., Isaac, J. L. & Fisher, D. O. (2007) Rarity of a top predator triggers continent-wide collapse of mammal prey: dingoes and marsupials in Australia. Proceedings of the Royal Society B 274, 341-346.

Members (External)

Prof Chris Johnson, c.n.johnson@utas.edu.au

Dr Menna Jones, menna.jones@utas.edu.au