Landscape-scale conservation planning in a changing climate : a koala case study

Abstract

ABSTRACT The extinctions of species and the decline of biodiversity due to human-induced habitat loss and landscape fragmentation continue globally. Compounding these threats is rapid anthropogenic climate change, which will cause many species and their habitats to experience shifts in their distributions and even extinctions. For effective conservation planning, it is critical we understand where these climate change-induced range shifts are likely to occur, which are co-occurring with existing stressors and what we can do to try and help solve this problem. There are now many modelling techniques and conservation planning tools that can provide quantitative and robust information to support conservation planning decisions under future climate change. The aim of this thesis was to advance the understanding of how the distributions of species and their essential habitats will shift in response to climate change, so that conservation planning resources can be invested most effectively. This was achieved by using the koala (Phascolarctos cinereus) as a case study species. I chose the koala because it is a wide-ranging endemic specialist folivore that is vulnerable to land clearing and anthropogenic climate change. The koala family (Phascolarctidae) has an ancient history of adaptation to the Australian landscape and climate that has spanned tens of millions of years and incorporated numerous genera and species. Today, P. cinereus is the only remaining member of this ancient family and its future survival in the wild is becoming increasingly tenuous. This project applied landscape-scale species distribution modelling techniques and a conservation prioritisation framework to explore the past, present and future distribution of the koala. Firstly, I investigated the fossil records of koalas to ascertain their historical distribution and found that in the past, koalas have inhabited areas of Australia such as Central and Western Australia, where they no longer occur. Using bioclimatic modelling, I developed a ‘climate envelope’ for koalas and found that modern koalas occur at a temperature range of -4 oC to 37.7 oC (mean annual 16.4 oC) and an annual precipitation range of 234 to 2480 mm (mean annual 863 mm). I then examined their potential distribution, or climate refugia, at the Last Glacial Maximum and showed that their core range contracted significantly to small areas of southeast Queensland and northern New South Wales. Secondly, species distribution modelling was undertaken for koalas throughout their modern range in eastern Australia and under a range of future climate change scenarios. I found that their distribution will contract progressively eastwards and southwards under climate change and koalas will disappear from their western regions. The highest probability of koala presence occurred between mean maximum summer temperatures of 23 oC and 26 oC and mean annual rainfall of between 700 and 1500 mm and the most important variable was mean maximum summer temperatures. Finally, for the state of Queensland, a prioritisation analysis was applied to identify the local government area districts that are the highest priority for conservation resources. To do this I used species distribution models predicting the probability distributions of koalas and their critical food and habitat resources in Queensland, under current and future climate change scenarios. These probability models were used as habitat layers to identify priority local government areas, using the conservation planning software Zonation for four scenarios based on: 1) koalas predicted distribution under the current climate, 2) koalas and their major food trees predicted distributions under the current climate, 3) koalas and their major food trees predicted distributions under current, 2030 and 2050 climates and 4) koalas and their major food trees predicted distributions under the 2050 climate. It was important to use this combination of scenarios so that the effects of including the koala food trees in the prioritisation analysis could be ascertained. By 2050, the potential overlaps between predicted koala distributions and their critical food trees were reduced, with koalas in western regions contracting further eastwards than their key food tree E. camaldulensis (river red gum). By 2070, the koala and two key food trees, E. tereticornis, (forest red gum) and E. crebra, (narrow-leaved ironbark) were limited to a narrow zone of coastal southeast Queensland. By 2050, there was a decrease in priority western areas and a general concentration of priority areas in the more costly and rapidly urbanising southeast Queensland regions, therefore posing significant conservation investment challenges. This thesis makes an important contribution to furthering the understanding of the impact of climate change on species and their habitats, by simultaneously modelling a specialist folivore and its essential eucalypt food trees. It demonstrates a novel quantitative approach to deciding where conservation planning resources should be invested, for a species dependent on a specialised habitat requirement, to gain the most effective conservation planning outcomes, particularly under climate change