Department of Natural Resource Sciences, McGill University, Macdonald Campus, H9X3V9 QC, Canada.
Integr Comp Biol. 2011 Sep;51(3):419-31. doi: 10.1093/icb/icr059. Epub 2011 Jun 22.
If heat generated through activity can substitute for heat required for thermoregulation, then activity in cold environments may be energetically free for endotherms. Although the possibility of activity-thermoregulatory heat substitution has been long recognized, its empirical generality and ecological implications remain unclear. We combine a review of the literature and a model of heat exchange to explore the generality of activity-thermoregulatory heat substitution, to assess the extent to which substitution is likely to vary with body size and ambient temperature, and to examine some potential macroecological implications. A majority of the 51 studies we located showed evidence of activity-thermoregulatory heat substitution (35 of 51 studies), with 28 of 32 species examined characterized by substitution in one or more study. Among studies that did detect substitution, the average magnitude of substitution was 57%, but its occurrence and extent varied taxonomically, allometrically, and with ambient temperature. Modeling of heat production and dissipation suggests that large birds and mammals, engaged in intense activity and exposed to relatively warm conditions, have more scope for substitution than do smaller endotherms engaged in less intense activity and experiencing cooler conditions. However, ambient temperature has to be less than the lower critical temperature (the lower bound of the thermal neutral zone) for activity-thermoregulatory heat substitution to occur and this threshold is lower in large endotherms than in small endotherms. Thus, in nature, substitution is most likely to be observed in intermediate-sized birds and mammals experiencing intermediate ambient temperatures. Activity-thermoregulatory heat substitution may be an important determinant of the activity patterns and metabolic ecology of endotherms. For example, a pattern of widely varying field metabolic rates (FMR) at low latitudes that converges to higher and less variable FMR at high latitudes has been interpreted as suggesting that warm environments at low latitudes allow a greater variety of feasible metabolic niches than do cool, high-latitude environments. However, activity-thermoregulatory heat substitution will generate this pattern of latitudinal FMR variation even if endotherms from cold and warm climates are metabolically and behaviorally identical, because the metabolic rates of resting and active animals are more similar in cold than in warm environments. Activity-thermoregulatory heat substitution is an understudied aspect of endotherm thermal biology that is apt to be a major influence on the physiological, behavioral and ecological responses of free-ranging endotherms to variation in temperature.
如果活动产生的热量可以替代体温调节所需的热量，那么在寒冷环境中活动对恒温动物来说可能是无需消耗能量的。尽管活动-体温调节热替代的可能性早已被认识到，但它的普遍适用性和生态意义仍不清楚。我们结合文献综述和热交换模型来探讨活动-体温调节热替代的普遍性，评估替代的程度可能随体型和环境温度的变化而变化，并研究一些潜在的宏观生态意义。我们定位的 51 项研究中有一大部分显示出活动-体温调节热替代的证据（51 项研究中有 35 项），在所检查的 32 个物种中有 28 个在一个或多个研究中表现出替代。在检测到替代的研究中，替代的平均幅度为 57%，但其发生和程度在分类学上、异速生长上和环境温度上有所不同。热产生和耗散的建模表明，与从事低强度活动和经历凉爽条件的较小恒温动物相比，从事高强度活动和暴露于相对温暖条件的大型鸟类和哺乳动物有更多的替代空间。然而，环境温度必须低于下限临界温度（热中性区的下限），活动-体温调节热替代才能发生，而且这个阈值在大型恒温动物中比在小型恒温动物中更低。因此，在自然界中，替代最有可能在中等体型的鸟类和哺乳动物中观察到，它们经历中等的环境温度。活动-体温调节热替代可能是恒温动物活动模式和代谢生态学的一个重要决定因素。例如，在低纬度地区广泛变化的场代谢率（FMR）模式在高纬度地区趋于更高且变化较小的 FMR，这种模式被解释为表明低纬度地区温暖的环境比凉爽的高纬度环境允许更多可行的代谢小生境。然而，即使来自寒冷和温暖气候的恒温动物在代谢和行为上完全相同，活动-体温调节热替代也会产生这种纬度 FMR 变化的模式，因为在寒冷环境中，静止和活动动物的代谢率比在温暖环境中更相似。活动-体温调节热替代是恒温动物热生物学中一个研究不足的方面，它很可能是自由生活的恒温动物对温度变化的生理、行为和生态反应的主要影响因素。
