Mechanistic models of terrestrial ectotherms predict that climate warming will induce activity restriction due to heat stress and loss of shade, leading to the extinction of numerous populations. Such models rely on the assumption that activity patterns are dictated by simple temperature thresholds independent of changes in water availability. However, changes in water availability may further influence thermoregulation behavior of ectotherms through dehydration risk perception, changes in water balance or changes in microclimatic conditions. Here, we experimentally assess the interactive effects of thermal conditions and water availability on activity patterns, shade selection and thermoregulation efficiency in a model ectothermic species. Thermoregulation behavior of adult common lizards (Zootoca vivipara) was monitored in outdoor mesocosms as we manipulated water availability, providing water as mist in the morning and free-standing water during the daytime. We recorded operative temperatures and micro-meteorological conditions to infer thermal constraints and dehydration risk. Activity and shade selection were better predicted by continuous changes in thermal conditions and dehydration risk, respectively, than by threshold functions. In addition, water supplementation increased activity in males and reduced shade selection in both sexes, most probably as a behavioral response to the perception of a stronger dehydration risk. Water supplementation also influenced the thermal quality of the environment, which in turn altered daily activity patterns and thermoregulation statistics. This demonstrates that dual effects of heat and water stress on activity patterns may lead to stronger activity restriction as a result of climate change than currently predicted.

中文翻译：

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水分可用性的短期变化影响干性皮肤变温动物的体温调节行为

陆地外温动物的机制模型预测，气候变暖将由于热应激和遮荫消失而导致活动受限，导致众多种群灭绝。此类模型依赖于以下假设：活动模式由与可用水量变化无关的简单温度阈值决定。然而，可用水量的变化可能会通过脱水风险感知、水平衡的变化或小气候条件的变化进一步影响变温动物的体温调节行为。在这里，我们通过实验评估热条件和可用水量对模型变温物种的活动模式、阴影选择和温度调节效率的交互影响。当我们控制水的可用性时，我们在室外中层环境中监测了成年普通蜥蜴（Zootoca vivipara）的体温调节行为，早上提供水雾，白天提供独立水。我们记录了操作温度和微气象条件，以推断热限制和脱水风险。与阈值函数相比，热条件和脱水风险的连续变化分别可以更好地预测活动和阴影选择。此外，补水增加了雄性的活动，减少了两性的遮荫选择，这很可能是对更强脱水风险感知的行为反应。补水还影响环境的热质量，进而改变日常活动模式和体温调节统计数据。