Conserving Koalas in the 21st Century: Synthesising the Dynamics of Australia’s Koala Populations

Brief description

We conducted a four-step Delphi expert elicitation procedure. This approach allowed us to address the gaps in knowledge regarding national koala populations with the robustness of collective judgement. The four steps of the Delphi method ask for an upper estimate, a lower estimate, a best guess and a percentage confidence interval. Prior to the commencement of the workshop, the participants were required to complete the first round of the questionnaire. These results were then re-evaluated during the workshop and a second round of elicitation was conducted. The outcome of the two workshops will be a synthesis of the distribution and abundance of koalas, population trends, and a region-specific summary of threats to koalas. Peer-reviewed journal publications will be produced. The information will be used to inform researchers, managers and decision-makers to ensure that viable koala populations persist across their natural range.

Lineage

Workshop 1 scoped the issues and developed the methods for synthesising the available data and expert knowledge. This allowed, for the first time, a unified examination and synthesis of what data were available, where there were gaps in knowledge, what existing analyses have shown, and the opportunity to re-examine data in a new light.

Prior to the workshop, all available data on koala numbers and trends held by koala researchers, government agencies and community groups from the various biogeographic regions where koalas occur were identified and assembled. The outcome of this activity was a systematic evaluation of the regional trends in koala abundance and the factors influencing koala population decline or increase.

It was found that New South Wales and Queensland have natural koala populations, while central and western Victoria and South Australia have introduced populations. The south Gippsland population of Victoria is a natural population with high genetic diversity, and requires a different management approach. The introduced populations are considered stable, although several overabundant (e.g. Mt. Eccles and Kangaroo Island) are subject to managed declines. The prognosis for these populations was for continued stability, but becoming increasing vulnerable to land use pressures and extreme events such as droughts and bushfires.

The evidence presented indicated that koala populations of coastal and western Queensland are mostly declining, although some low density populations (e.g. Oakey, eastern Darling Downs) are relatively stable. The most pronounced population declines are in southeast Queensland, where urban development has destroyed and fragmented large areas of high quality koala habitat, with resulting increases in mortality from vehicle collisions, dog attacks and disease. In the past 20 years, there have been substantial population declines in the Mulglands of southwest Queensland and in central Queensland due to drought, heat waves and land clearing. These populations are particularly vulnerable to projected changes in climate. In central and southern inland Queensland, coal and coal seam gas resource developments and associated infrastructure pose a new threat. The long-term prognosis for Queensland populations is for contracting populations in western regions and urbanising coastal regions, with some low-density sub-coastal rural populations remaining relatively stable.

New South Wales populations are subject to similar trends and threats. Populations in urbanising coastal regions are declining, with some coastal populations (e.g. Eden and Iluka) declining towards local extinction. However, there are several populations (e.g. Lismore, Campbelltown, Southern Highlands) which appear to be relatively stable. In northwest New South Wales, the Pilliga forest population has experienced a sharp decline in the past decade due to drought and wildfire, while the Gunnedah population declined sharply in 2009 due to drought and heat wave. Both populations are facing new pressures from coal and coal seam gas resource developments. It was found that more information is needed on the status of populations in protected areas in New South Wales.

Workshop 2 extended on Workshop 1 and involved the same personnel who served as the expert panel. The workshop involved filling in the gaps in the empirical data from Workshop 1 using novel expert elicitation methods. Expert elicitation methods have been demonstrated to effectively capture experts’ opinion, particularly within an expert’s region of knowledge (Martin et al. 2005; Murray et al. 2009). The Australian Centre for Ecological Analysis and Synthesis or ACERA Elicitation Software Tool (ACERA 2010) was used for this activity.

The Working Group elicitation process took place in the context of a facilitated Risk Analysis Workshop using the DELPHI process for complex decision‐making (Burgman 2005). This approach allowed the group to address the gaps in knowledge regarding national koala populations with the robustness of collective judgment. The four steps of the Delphi method asked for an upper estimate, a lower estimate, a best guess and a percentage confidence interval (in the range 50-100%). Prior to the commencement of the workshop, the participants were required to complete the first round of the questionnaire. These results were then re-evaluated during the workshop and a second round of elicitation was conducted.

The outcome of the two workshops was a bioregional synthesis of the distribution and abundance of koalas, population trends, and a summary of threats to koalas.

The pooled opinion from the 15 experts found that koalas have declined by 30% to more than 50% across most of Queensland’s bioregions, including inland areas such as the Mulgalands and coastal regions such as southeast Queensland. Koalas in New South Wales have declined to a similar extent, particularly in northern coastal bioregions. In nearly all other bioregions they have declined by levels ranging 15% - 50%. In Victoria and South Australia, introduced koala populations have declined by 15-30%, although in some areas around the Mt. Lofty Ranges and eastern Gippsland, populations have increased by up to 24%.

The mean koala population for Queensland was estimated to be approximately 78,000, for New South Wales/ACT approximately 36,000, for Victoria approximately 182,000 and for South Australia approximately 33,000.

These findings highlight the disparity between koala population demographics in the northern states compared with the southern states, where koalas were historically culled to virtual extinction for the fur trade but have survived in ‘island’ habitats. The more abundant southern koala populations however, are not necessarily secure due to problems with over browsing, low genetic diversity, habitat loss and in more recent times, disease.

Progress Code: completed

Maintenance and Update Frequency: notPlanned

Notes

Credit
We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
This work was funded by ACEAS, a facility of Terrestrial Ecosystem Research Network (TERN), an Australian Government National Collaborative Research Infrastructure Strategy (NCRIS) project.