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.物种的分布范围受生物体对气候条件的生理耐受限度约束。通过纳入生理约束条件，物种分布模型（species distribution models）可揭示生物与非生物因子如何限制物种的地理分布范围。水分散失速率会影响物种分布，但对个体水分散失的表征需要复杂计算。皮肤水分散失阻力（skin resistance to water loss, ri）被认为是反映水分散失速率最具信息量的指标，因为它可抵消实验偏差的影响。然而，计算ri需要借助生物物理方程求解生物体周围空气的阻力，即边界层阻力（boundary layer resistance, rb）。 本研究对比了野外采集的无肺螈属（Plethodon）蝾螈皮肤水分散失阻力的理论测量方法与经验测量方法。在经验方法中，我们依托流式系统（flow through system），在5个体型梯度、2个温度水平、3个水汽压亏缺条件以及6个流速梯度下，测定了琼脂复制品的rb值。同时，我们在相同实验条件下通过生物物理方程计算rb值。随后，我们探究了将皮肤阻力与边界层阻力纳入物种分布模型后的生态学意义——该模型可估算研究物种整个地理分布范围内的潜在觅食时长与能量平衡。 研究发现，采用经验方法计算rb时会得到负的ri值，而生物物理计算则可得到具有生物学意义的ri值。物种分布模型结果显示，纳入边界层阻力与皮肤阻力后，模型全域范围内的平均能量平衡估算值最高提升70%，潜在觅食时长提升92%。我们据此认为，使用琼脂复制品表征皮肤水分散失阻力的方法并不恰当，而纳入水分散失的边界层阻力与皮肤阻力，可优化机制性物种分布模型（mechanistic species distribution models）的活动与能量学估算结果。更重要的是，本研究表明，纳入水分散失速率背后的物理过程，能够改善诸多动物类群的生境适宜性（habitat suitability）估算结果。