Data from: Body temperature, heart rate, and activity patterns of two boreal homeotherms in winter: homeostasis, allostasis, and ecological coexistence

Organisms survive environmental variation by combining homeostatic
regulation of critical states with allostatic variation of other traits,
and species differences in these responses can contribute to coexistence
in temporally-variable environments. In this paper, we simultaneously
record variation in three functional traits – body temperature (Tb), heart
rate, and activity - in relation to three forms of environmental variation
– air temperature (Ta), photoperiod, and experimentally-manipulated
resource levels – in free-ranging snowshoe hares and North American red
squirrels to characterize distinctions in homeotherm responses to the
extreme conditions of northern boreal winters. Hares and squirrels
differed in the level and precision of Tb regulation, but also in the
allostatic pathways necessary to maintain thermal homeostasis. Hares
demonstrated a stronger metabolic pathway (through heart rate variation
reflective of the thermogenesis), while squirrels demonstrated a stronger
behavioral pathway (through activity variation that minimizes cold
exposure). As intermediate-sized, winter-active homeotherms, hares and
squirrels share many functional attributes, yet, through the integrated
monitoring of multiple functional traits in response to shared
environmental variation, our study reveals many pairwise species
differences in homeostatic and allostatic traits, that both define and are
defined by the natural history, functional niches, and coexistence of
sympatric species.

生物体通过将关键状态的稳态调节（homeostatic regulation）与其他性状的应变稳态变异（allostatic variation）相结合，在环境波动中存活；而此类响应的物种间差异，可促进临时波动环境中的物种共存。
本研究同步记录了3种功能性状——体温（Tb）、心率与活动水平——的变异，并将其与3类环境波动因子——空气温度（Ta）、光周期与实验操控的资源供给水平——关联分析，研究对象为自由栖息的野生雪兔与北美红松鼠，旨在刻画恒温动物（homeotherm）应对北方寒带冬季极端环境的响应差异。
雪兔与红松鼠不仅在体温调节的水平与精度上存在差异，在维持体温稳态所需的应变稳态通路上亦有所不同。
雪兔展现出更强的代谢通路——其通过反映产热活动的心率变异实现——而红松鼠则展现出更强的行为通路——其通过减少寒冷暴露的活动水平变异实现。
作为体型中等、冬季活跃的恒温动物，雪兔与红松鼠共享诸多功能属性；但本研究通过对多种功能性状响应共同环境波动的整合监测，揭示了二者在稳态与应变稳态性状间的诸多差异——这些差异既界定了同域分布物种（sympatric species）的自然历史、功能生态位与共存模式，同时也由这些因素所塑造。