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Threatening processes

Modelling climate-change-induced shifts in the distribution of the koala

Adams-Hosking, C, Grantham, HS, Rhodes, JR, McAlpine, C & Moss, PT 2011, Wildlife Research, vol. 38, pp. 122-130.

Climate change is resulting in shifting distributions of koala populations throughout Australia as a direct result of increased temperatures and decreased rainfall. Bioclimatic models based on current koala localities and several climate change scenarios were used in this study to predict future climatic envelopes of koala populations. Results showed a likely progressive movement eastwards and southwards in Queensland, New South Wales and Victoria.

  To model continuous and categorical pre-existing data, Maxent software was applied, which uses a maximum-entropy or ‘optimal’ approach for modelling species niches and distributions. The data applied to this model included koala occurrence data for approximately the last 100 years. A 10km grid system was applied to these datasets, meaning that one record could be selected from each grid, to reduce geographical bias in highly populated areas. In addition, climate data was used to model the current climatic koala envelopes and consisted of baseline gridded data of a combination of mean maximum summer temperatures and mean annual rainfall from 1961-1990.  Climate predictions were based on the CSIRO MK 3.5 climate model derived from OzClim with additional scenarios incorporated into the model using the SRES A1F1 high emission scenario group devised by the IPCC AR4, to consider possible future global social, economic and environmental changes. Overall, a fitted model was produced and developed at a 10 km2 resolution showing the current climatic envelope of koala populations, with the highest likelihood of koala presence in areas with mean maximum summer temperatures of 23 to 26oC and mean annual rainfall of between 700-1500 mm and highest probability of predicted populations in eastern Australia. When climate change scenarios were applied and fitted to the same model, however, results showed progressive eastward movements of koala populations by 2030 and then increasingly south by 2050 and 2070, with the highest presence shifting to eastern New South Wales, eastern Victoria and Tasmania.

  The magnitude and shift in geographical distributions of koalas is evident in this study as it shows a rapid change in distribution due to a hotter and drier climate in Australia. The Maxent predictions outline possible refuge areas suitable for koala populations according to these climate change scenarios; however, do not outline the quality of habitat in these regions, or take into consideration extreme weather events such as bushfires, or regional droughts, which may potentially all increase. In addition, it is important to note that koalas do not yet occur in some areas predicted by the model. Migration to isolated regions listed as potential future habitats such as Tasmania would therefore require human-assisted translocation.

  This study highlights the importance of understanding the sensitivity of koalas to future climate change by outlining where populations are likely to contract and potentially shift. The authors highlight the importance of focusing conservation actions at a regional scale, particularly around these future predicted climate refugia in order to protect the species from possible extinction in certain areas of Australia.

 

Summarised by Robyn Boldy

 

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