Thermal adaptation best explains Bergmann's and Allen's rule across ecologically diverse shorebirds

Bergmann’s and Allen’s rules state that endotherms should be larger and have shorter appendages in cooler climates.  However, the drivers of these rules are not clear. Both rules could be explained by adaptation for improved thermoregulation, including plastic responses to temperature in early life. Non-thermal explanations are also plausible as climate impacts other factors that influence size and shape, including starvation risk, predation risk, and foraging ecology. We assess the potential drivers of Bergmann’s and Allen’s rules in 30 shorebird species using extensive field data (>200,000 observations). We show birds in hot, tropical northern Australia have longer bills and smaller bodies than conspecifics in temperate, southern Australia, conforming with both ecogeographical rules. This pattern is consistent across ecologically diverse species, including migratory birds that spend early life in the Arctic. Our findings best support the hypothesis that thermoregulatory adaptation ...伯格曼法则（Bergmann's Rule）与阿伦法则（Allen's Rule）提出，恒温动物（endotherm）在较为寒冷的气候中应拥有更大的体型与更短的附肢。然而，支撑这两大生态地理法则的具体驱动机制仍未明确。两种法则均可通过优化体温调节的适应性演化得到解释，其中包括个体在生命早期对温度产生的表型可塑性响应。此外，非温度驱动的解释同样合理，因为气候会影响诸多其他影响生物体型与形态的因素，包括饥饿风险、捕食风险与觅食生态。我们基于超过20万条野外观测数据，对30种滨鸟（shorebird）的伯格曼与阿伦法则潜在驱动机制展开评估。研究发现，与澳大利亚南部温带地区的同种个体相比，澳大利亚北部热带炎热区域的滨鸟拥有更长的喙部与更小的体型，这一结果符合两项生态地理法则的预测。这一规律在生态多样性丰富的类群中均成立，其中包括在北极度过生命早期阶段的候鸟。我们的研究结果最有力地支持了体温调节适应性演化的假说……