Use of expert knowledge to elicit population trends for the koala (Phascolarctos cinereus)
Christine Adams-Hosking1*, Marissa F. McBride2,3, Greg Baxter4, Mark Burgman5, Deidre de Villiers6, Rodney Kavanagh7, Ivan Lawler8, Daniel Lunney9,10, Alistair Melzer11, Peter Menkhorst12, Robyn Molsher13, Ben D. Moore14, David Phalen15, Jonathan R. Rhodes16,18, Charles Todd12, Desley Whisson17 and Clive A. McAlpine18
1 School of Geography, Planning and Environmental Management, Global Change Institute, The University of Queensland, Brisbane, Qld 4072, Australia
2 School of Botany, The University of Melbourne, Melbourne, Vic. 3010, Australia
3 Department of Biosciences, University of Helsinki, Helsinki 00014, Finland
4 School of Geography Planning and Environmental Management, The University of Queensland, Landscape Ecology and Conservation Group, Brisbane, Qld 4072, Australia
5 School of Botany, Environmental Science, The University of Melbourne, Melbourne, Vic. 3010, Australia
6 Endeavour Veterinary Ecology, 1695 Pumicestone Rd, Toorbul, Qld 4510, Australia
7 The Australian National University, Research School of Biology, Canberra 0200, Australia, Niche Environment and Heritage, PO Box 2443, North Parramatta, NSW 2150 Australia
8 Wildlife Heritage and Marine Division, Department of the Environment, Marine and Freshwater Species Conservation Section, Canberra ACT 2700, Australia
9 Ofﬁce of Environment and Heritage NSW, Hurstville, NSW 2220, Australia
10 School of Biological Sciences, University of Sydney, Sydney, NSW 2006, Australia
11 Koala Research Centre of Central Queensland, School of Medical and Applied Sciences, CQ University, Rockhampton, Qld 4702, Australia
12 Department of Environment, Land, Water & Planning, Arthur Rylah Institute for Environmental Research, Heidelberg, Vic. 3084, Australia
13 Department of Environment, Water and Natural Resources, PO Box 39, Kingscote, SA 5223, Australia,
14 Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, 2751 NSW, Australia
15 Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2006, Australia
16 ARC Centre of Excellence for Environmental Decisions, The University of Queensland, Brisbane, Qld 4072, Australia,
17 School of Life and Environmental Sciences, Faculty of Science Engineering & Built Environment, Deakin University, Burwood, Vic. 3125, Australia
18 Landscape Ecology and Conservation Group, School of Geography, Planning, and Environmental Management, The University of Queensland, Brisbane, Qld 4072, Australia
Aim The koala is a widely distributed Australian marsupial with regional populations that are in rapid decline, are stable or have increased in size. This study examined whether it is possible to use expert elicitation to estimate abundance and trends of populations of this species. Diverse opinions exist about estimates of abundance and, consequently, the status of populations.
Location Eastern and south-eastern Australia
Methods Using a structured, four-step question format, a panel of 15 experts estimated population sizes of koalas and changes in those sizes for bioregions within four states. They provided their lowest plausible estimate, highest plausible estimate, best estimate and their degree of conﬁdence that the true values were contained within these upper and lower estimates. We derived estimates of the mean population size of koalas and associated uncertainties for each bioregion and state.
Results On the basis of estimates of mean population sizes for each bioregion and state, we estimated that the total number of koalas for Australia is 329,000 (range 144,000–605,000) with an estimated average decline of 24% over the past three generations and the next three generations. Estimated percentage of loss in Queensland, New South Wales, Victoria and South Australia was 53%, 26%, 14% and 3%, respectively.
Main conclusions It was not necessary to achieve high levels of certainty or consensus among experts before making informed estimates. A quantitative, scientiﬁc method for deriving estimates of koala populations and trends was possible, in the absence of empirical data on abundances.
Keywords bioregions, Delphi process, expert elicitation, iconic, knowledge, koala populations, Phascolarctos cinereus, threatened species, uncertainty.