Data from: Physical calculations of resistance to water loss improve predictions of species range models

Species ranges are constrained by the physiological tolerances of organisms to climatic conditions. By incorporating physiological constraints, species distribution models can identify how biotic and abiotic factors constrain a species’ geographic range. Rates of water loss influence species’ distributions, but characterizing water loss for an individual requires complex calculations. Skin resistance to water loss (ri) is considered to be the most informative metric of water loss rates because it controls for experimental biases. However, calculating ri requires biophysical equations to solve for the resistance of the air that surrounds an organism, termed the boundary layer resistance (rb). Here, we compared theoretical and empirical methods for measuring skin resistance to water loss of a Plethodon salamander collected from nature. For the empirical methods, we measured rb of agar replicas at five body sizes, two temperatures, three vapor pressure deficits, and six flow rates using a flow through system. We also calculated rb using biophysical equations under the same experimental conditions. We then determined the ecological implications of incorporating skin and boundary layer resistance into a species range model that estimated potential foraging time and energy balance throughout the geographic range of the study species. We found that empirical methods for calculating rb resulted in negative values of ri, whereas biophysical calculations produced meaningful values of ri. The species range model determined that calculations of the boundary layer and skin resistances increased average estimates of energy balance by as much as 70% and potential foraging time by 92% throughout the spatial extent of the model. We conclude that the use of agar replicas is an inadequate technique to characterize skin resistance to water loss, and incorporating boundary and skin resistances to water loss improve estimates of activity and energetics for mechanistic species distribution models. More importantly, our study suggests incorporating the physical processes underlying rates of water loss could improve estimates of habitat suitability for many animals.