Determining range edges: habitat quality, climate or climate extremes?
Leonie Seabrook1, Clive McAlpine1, Jonathan Rhodes1, Greg Baxter1, Adrian Bradley2 and Daniel Lunney3
1The University of Queensland, Landscape Ecology and Conservation Group, School of Geography, Planning & Environmental Management, Brisbane, Qld 4072, Australia
2The University of Queensland, School of Biomedical Sciences, Brisbane, Qld 4072, Australia
3Ofﬁce of Environment and Heritage NSW, PO Box 1967, Hurstville, NSW 2220, Australia
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 species 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 experienced higher levels of rainfall during a decade-long drought. The spatial pattern 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 theoretical 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 species 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.