Department of Biology, Appalachian State University, Boone, North Carolina, USA.
Department of Biology, Indiana University, Bloomington, Indiana, USA.
J Anim Ecol. 2023 Jun;92(6):1149-1160. doi: 10.1111/1365-2656.13907. Epub 2023 Mar 22.
Ecogeographic rules describe spatial patterns in biological trait variation and shed light on the drivers of such variation. In animals, a consensus is emerging that 'pioneering' traits may facilitate range shifts via a set of bold, aggressive and stress-resilient traits. Many of these same traits are associated with more northern latitudes, and most range shifts in the northern hemisphere indicate northward movement. As a consequence, it is unclear whether pioneering traits are simply corollaries of existing latitudinal variation, or whether they override other well-trodden latitudinal patterning as a unique ecogeographic rule of phenotypic variation. The tree swallow Tachycineta bicolor is a songbird undergoing a southward range shift in the eastern United States, in direct opposition of the poleward movement seen in most other native species' range shifts. Because this organic range shift countervails the typical direction of movement, this case study provides for unique ecological insights on organisms and their ability to thrive in our changing world. We sampled female birds across seven populations, quantifying behavioural, physiological and morphological traits. We also used GIS and field data to quantify a core set of ecological factors with strong ties to these traits as well as female performance. Females at more southern expansion sites displayed higher maternal aggression, higher baseline corticosterone and more pronounced elevation of corticosterone following a standardized stressor, contrary to otherwise largely conserved latitudinal patterning in these traits. Microhabitat variation explained some quantitative phenotypic variation, but the expansion and historic ranges did not differ in openness, distance to water or breeding density. This countervailing range shift therefore suggests that pioneering traits are not simply corollaries of existing latitudinal variation, but rather, they may override other well-trodden latitudinal patterning as a unique ecogeographic rule of phenotypic variation.
生态地理规律描述了生物特征变异的空间模式，并揭示了这种变异的驱动因素。在动物中，人们越来越认为，“开拓性”特征可能通过一系列大胆、进取和抗压的特征来促进范围转移。这些特征中有许多与更北的纬度有关，而且北半球的大多数范围转移都表明向北移动。因此，目前尚不清楚开拓性特征是否仅仅是现有纬度变化的必然结果，还是它们是否超越了其他经过充分验证的纬度模式，成为表型变化的独特生态地理规律。斑胸草雀 Tachycineta bicolor 是一种鸣禽，正在美国东部进行向南的范围转移，与大多数其他本地物种的范围转移中看到的向极地移动直接相反。由于这种有机范围转移与典型的移动方向相反，这种案例研究为生物及其在我们不断变化的世界中茁壮成长的能力提供了独特的生态见解。我们在七个种群中对雌性鸟类进行了采样，量化了行为、生理和形态特征。我们还使用 GIS 和现场数据来量化与这些特征以及雌性性能密切相关的一系列核心生态因素。在更南部扩张地点的雌性表现出更高的母性攻击性、更高的基础皮质酮和在标准化应激源后皮质酮的升高更为明显，这与这些特征中其他基本一致的纬度模式相反。微生境变化解释了一些定量表型变异，但扩张和历史范围在开放性、与水的距离或繁殖密度方面没有差异。因此，这种相互抵消的范围转移表明，开拓性特征不仅仅是现有纬度变化的必然结果，而是可能超越其他经过充分验证的纬度模式，成为表型变化的独特生态地理规律。
