Abstract
<jats:p>Aim A key outcome of the global biodiversity crisis is the contraction and range shift of species distribution into refugial habitats that afford some level of protection against threatening processes. Range contractions driven by spatially overlapping threats may fragment populations to the point where functional habitat is lost. This study identifies a range contraction of the Vulnerable green and golden bell frog ( Ranoidea aurea) in south-east Australia using a multi-method approach. Location New South Wales Coastline, Australia Methods We fitted alpha hulls, species distribution models (SDMs; MaxEnt, Random Forest, Boosted Regression Trees, and an AUC-weighted ensemble) and conducted a hypervolume analysis to quantify drivers of change in the species’ range and ecological niche between full and contemporary periods. Results Findings show R. aurea has undergone niche contraction and displacement into coastal saline-influenced refugia. Our results demonstrated a 76% reduction in extent of occurrence, a suitable habitat reduction of ~96% between long-term and contemporary periods, and an environmental niche contraction of 57%. Remaining habitat was strongly associated with coastal proximity with centroid shifts towards more saline and slightly less humid environments. Main conclusions The concentration of R. aurea in coastal regions suggests intensified dependence on coastal refugia, persisting in salt-exposed habitat that may act to suppress chytrid fungus. Yet, the threat abatement afforded by low-lying, saline coastal environments is wedging R. aurea into chytrid refugia that is at risk from sea level rise. This refugial squeeze is likely to be a global phenomenon that highlights the value of integrating geometric and probabilistic niche approaches with SDMs to resolve temporal contraction in species distributions. Protection of such zones in the face of sea level rise will ultimately determine the future range and population viability of species. Keywords Ranoidea aurea, Chytrid fungus, Coastal wetlands, Range contraction, Suboptimal refugia, Spatial relationships, Climate change.</jats:p>