Data from: Biophysical modeling of the temporal niche: from first principles to the evolution of activity patterns

Most mammals can be characterized as nocturnal or diurnal. However infrequently, species may overcome evolutionary constraints and alter their activity patterns. We modeled the fundamental temporal niche of a diurnal desert rodent, the golden spiny mouse, Acomys russatus. This species can shift into nocturnal activity in the absence of its congener, the common spiny mouse, A. cahirinus, suggesting that it was competitively driven into diurnality, and that this shift in a small desert rodent may involve physiological costs. Therefore, we compared metabolic costs of diurnal vs. nocturnal activity using a biophysical model to evaluate the preferred temporal niche of this species. The model predicted that energy expenditure during foraging is almost always lower during the day except during mid-day in summer at the less sheltered microhabitat. We also found that a shift in summer to foraging in less sheltered microhabitats in response to predation pressure and food availability involves a significant physiological cost moderated by midday reduction in activity. Thus adaptation to diurnality may reflect the 'ghost of competition past'; Climate-driven diurnality is an alternative but less likely hypothesis. While climate is considered to play a major role in the physiology and evolution of mammals, this is the first study to model its effect on the evolution of activity patterns of mammals.绝大多数哺乳动物可被归类为夜行性或昼行性物种。但极少数情况下，物种能够突破演化限制，改变自身的活动节律模式。本研究针对一种昼行性沙漠啮齿动物——金刺鼠（Acomys russatus）的基础时间生态位（temporal niche）开展了建模分析。该物种在其同属近缘物种普通刺鼠（A. cahirinus）缺失的情况下，可转换为夜行性活动模式，这表明金刺鼠的昼行性是受种间竞争驱动形成的，且这类小型沙漠啮齿动物的活动节律转变可能伴随生理代价。为此，本研究借助生物物理模型（biophysical model）比较了昼行与夜行活动的代谢成本，以此评估该物种偏好的时间生态位。模型预测，除夏季正午于遮蔽度较低的微生境（microhabitat）中活动外，日间觅食的能量消耗几乎始终低于夜间。本研究还发现，夏季为应对捕食压力与食物可获得性，转而在遮蔽度较低的微生境中觅食，这一行为会伴随显著的生理代价，而该代价可通过正午减少活动量得到缓解。由此可见，对昼行性的适应或可反映“过往竞争的遗留效应”；而气候驱动的昼行性假说虽为备选解释，但可能性较低。尽管气候被认为对哺乳动物的生理机能与演化过程具有重要影响，但本研究仍是首个针对气候对哺乳动物活动节律演化的影响开展建模分析的研究。