BIODIVERSITY RESEARCH Determining range edges: habitat quality, climate or climate extremes? Leonie Seabrook 1 *, Clive McAlpine 1 , Jonathan Rhodes 1 , Greg Baxter 1 , Adrian Bradley 2 and Daniel Lunney 3† 1 The University of Queensland, Landscape Ecology and Conservation Group, School of Geography, Planning & Environmental Management, Brisbane, Qld 4072, Australia, 2 The University of Queensland, School of Biomedical Sciences, Brisbane, Qld 4072, Australia, 3 Office of Environment and Heritage NSW, PO Box 1967, Hurstville, NSW 2220, Australia *Correspondence: Leonie Seabrook, Environmental Decisions Group, School of Biological Sciences, The University of Queensland, Brisbane, Qld 4072, Australia. E-mail: l.seabrook@uq.edu.au † Present address: Environmental Decisions Group, The University of Queensland, School of Biological Sciences, Brisbane, Qld, 4072, Australia ABSTRACT Aim Climate change is predicted to adversely affect wildlife populations at the trailing edge of their range, with extreme weather events acting as a catalyst for local extinctions and range contractions. We assessed the relative importance of long-term climate averages, short-term drought and habitat in predicting spe- cies occupancy and range edge, using the koala (Phascolarctos cinereus) as a case study. Location Queensland, Australia. Methods We used mixed effects models to quantify the influence of habitat quality and climate on koala distribution at the trailing edge of their range, at three spatial scales. We used piecewise logistic regression to estimate thresholds in the relationship between the range edge and key environmental variables. Results Both climatic and habitat variables explained koala presence. At the site scale, the quality of habitat was important within landscapes that had expe- rienced higher levels of rainfall during a decade-long drought. The spatial pat- tern of the koala’s present-day western range limit reflects closely a breakpoint of ~350 mm in summer rainfall during the drought years, supporting both the- oretical predictions and empirical research on the influence of climate extremes on contracting edge populations. Main conclusions The distribution of fauna at their range margin in semi-arid regions reflects extreme climate events, such as drought. Within suitable climate conditions, habitat quality is important in determining site occupancy. The identification and protection of habitat refugia, where local microclimates and habitat characteristics can mitigate the impacts of extreme events on fauna spe- cies at the contracting edge of the range, may allow species to persist for longer under changing climate conditions. Keywords Distribution, Drought, Habitat quality, Koala, Range contraction, Trailing edge. INTRODUCTION Climate change is predicted to have major consequences for the world’s biodiversity, with shifts in species’ ranges and increasing rates of extinction (Parmesan & Yohe, 2003; Bel- lard et al., 2012). The effects of climate-induced range shifts on trailing and leading edge populations will be markedly different (Thuiller et al., 2008; Anderson et al., 2009). Lead- ing edge populations may migrate into new areas as climate conditions become more favourable, while trailing edge populations become increasingly fragmented and susceptible to local extinction as conditions become less favourable (Par- mesan & Yohe, 2003; Pearson et al., 2009; Thomas, 2010). A review of responses to recent climate change suggests that although species are adapting to global warming through evolutionary or range shifts, these adaptations are unlikely to prevent population declines for many species (Parmesan, 2006). To predict and manage changes in the distribution of a particular species over coming decades, it is important to identify the specific limiting factors at the range edge. The distribution of a species is the occupied part of the geographical area or range within which conditions are DOI: 10.1111/ddi.12152 ª 2013 John Wiley & Sons Ltd http://wileyonlinelibrary.com/journal/ddi 95 Diversity and Distributions, (Diversity Distrib.) (2014) 20, 95–106 A Journal of Conservation Biogeography Diversity and Distributions