Fire-driven loss of thermal refugia: hidden costs of habitat simplification for reptiles in the Murray Mallee

Full description

Fire shapes both habitat structure and fauna responses, but the link between these dynamics is poorly understand. This thesis examines how fire alters community composition, shelter availability, microclimates, and physiological performance in the reptiles of South Australia’s Murray Mallee. Long-term community data showed that reptile community composition not was not only shaped by fire, but contingent on the dynamics of individual fire events, and the microhabitats affected by fire. Field surveys demonstrated that fire simplified ground-layer vegetation and reduced the structural complexity and availability of shelters, particularly spinifex. Temperature measurements across fire ages and refuge sites revealed that recently burnt habitats were hotter, more variable, and less capable of buffering reptiles from extreme conditions. Biophysical modelling showed that these changes shortened activity windows, increased energetic costs, and raised the risk that operative temperatures exceeded physiological limits during hot weather, demonstrating severe constraints imposed by fire that are otherwise obscured by merely using occurrence data. Telemetry and physiological measurements indicated that reptiles occupying burnt habitat faced constrained refuge use, altered movement and thermoregulation, and declining body condition through time. Collectively, these findings identify thermal refuge loss as a mechanism linking fire-driven habitat simplification to reptile vulnerability. As fire frequency and heat extremes increase under climate change, conserving structurally complex, long-unburnt habitat and maintaining mosaics that retain refugia will be critical for sustaining reptile populations in semi-arid landscapes. Long unburnt microhabitats such as spinifex tussocks and leaf litter mats should therefore be treated as ecological assets, and explicitly conserved under future fire management practices with the goal of preserving these critical thermal refugia.