No abstract

Thermal acclimation is hypothesized to offer a selective advantage in seasonal habitats and may underlie disparities in geographic range size among closely‐related species with similar ecologies. Understanding this relationship is also critical for identifying species that are more sensitive to warming climates. Here, we study North American plethodontid salamanders to investigate whether acclimation ability is associated with species’ latitudinal extents and the thermal range of the environments they inhabit. We quantified variation in thermal physiology by measuring standard metabolic rate (SMR) at different test and acclimation temperatures for 16 species of salamanders with varying latitudinal extents. A phylogenetically‐controlled Markov chain Monte Carlo generalized linear mixed model (MCMCglmm) was then employed to determine whether there are differences in SMR between wide‐ and narrow‐ranging species at different acclimation temperatures. In addition, we tested for a relationship between the acclimation ability of species and the environmental temperature ranges they inhabit. Further, we investigated if there is a trade‐off between critical thermal maximum (CTMax) and thermal acclimation ability. MCMCglmm results show a significant difference in acclimation ability between wide and narrow‐ranging temperate salamanders. Salamanders with wide latitudinal distributions maintain or slightly increase SMR when subjected to higher test and acclimation temperatures, whereas several narrow‐ranging species show significant metabolic depression. We also found significant, positive relationships between acclimation ability and environmental thermal range, and between acclimation ability and CTMax. Wide‐ranging salamander species exhibit a greater capacity for thermal acclimation than narrow‐ranging species, suggesting that selection for acclimation ability may have been a key factor enabling geographic expansion into areas with greater thermal variability. Further, given that narrow‐ranging salamanders are found to have both poor acclimation ability and lower tolerance to warm temperatures, they are likely to be more susceptible to environmental warming associated with anthropogenic climate change.

Aim We tested the hypothesis that areas that acted as historical refugia during restrictive climate regimes currently harbour higher levels of biodiversity than areas that lacked refugia. Location The rain forests of Australia's Wet Tropics, the largest remaining fragments of the humid forest habitats that once covered the Australian continent. Methods We generated a model of climatic suitability for arachnids in the genus Austropurcellia, a group of small, dispersal‐limited mite harvestmen that are found throughout the Wet Tropics. We then projected this model onto palaeoclimate data layers from time slices going back to the Last Glacial Maximum and summed suitability over time to arrive at a measure of stability. We compared the power of metrics of present and past climatic suitability and stability to predict diversity (species richness and phylogenetic diversity) across subregions of the Wet Tropics. Results We found statistically significant correlations between measures of diversity (species richness and phylogenetic diversity) and present climatic suitability, LGM climatic suitability and our stability metric across subregions of the Wet Tropics. Although stability lost predictive power when analyses were corrected for spatial autocorrelation, and present‐day mean climatic suitability lost predictive power when corrected for spatial autocorrelation under one of our geographical binning schemes, mean climatic suitability during the Last Glacial Maximum had a positive and significant relationship to both number of species and phylogenetic diversity in all analyses. Main Conclusions Our results support a model of biodiversity preservation within historical refugia, resulting in higher present‐day diversity in refugial areas than in non‐refugial areas. Although previous studies of the Wet Tropics biota have demonstrated a relationship between habitat stability and diversity, ours is the first such study to consider phylogenetic diversity in addition to number of species.