Data from: Darker where cold and wet: Australian birds follow their own version of Gloger's rule

Gloger's rule is usually interpreted as predicting darker coloured animals in warmer and more humid/vegetated regions. The relative importance of temperature and rainfall or vegetation is however unclear, and often only one variable is tested at a time, mainly through proxies. Here, I assess the predictions of Gloger's rule for interspecific achromatic plumage variation (dark to light variation) for an entire avifauna (551 species of Australian landbirds). I tested the effects of climatic variables (temperature and rainfall) and vegetation structure on plumage reflectance at species and assemblage level (100x100 km cells), controlling for phylogenetic relatedness and spatial autocorrelation. To assess the robustness of these results I compared observed results with those of a null distribution of effects obtained from repeatedly simulating random plumage reflectance evolution on the phylogeny. At both the species and assemblage level, darker coloured birds were found in wetter and colder regions and in more densely vegetated habitats. Simulations confirm results at the species level and the effect of temperature at the assemblage level, but rainfall and vegetation effects at the assemblage level fall within the distribution of simulated effects and should be interpreted with care. Interspecific colour variation in Australian birds supports Gloger's rule for rainfall/vegetation, but shows the opposite pattern for temperature. Darker colours in wet and vegetated environments are consistent with the role of melanin pigmentation in preventing feather degradation by bacteria, but also with background-matching for camouflage. Darker plumage might be beneficial in colder regions or detrimental in warmer regions if it affects thermoregulation, a selective force often only assumed to be of importance for ectotherms. The data highlight the need to test the generality of biogeographic rules across levels and at broad scale. Experimental work is needed to confirm the mechanisms linking plumage achromatic variation to climate.

格洛杰法则（Gloger's rule）通常被阐释为：在更温暖、更湿润或植被更茂密的区域，动物体色更深。然而，温度与降雨量或植被的相对重要性尚不明确，且相关研究往往仅单次检验单一变量，且多通过替代指标开展。本研究针对整个澳大利亚陆地鸟类区系（551种陆地鸟类）的种间非彩色羽色变异（即从深色到浅色的色调变化），检验格洛杰法则的预测效力。研究分别在物种和群落水平（以100×100千米的栅格为单元），检验气候变量（温度、降雨量）与植被结构对羽色反光率的影响，并控制了系统发育亲缘关系与空间自相关效应。为评估结果的稳健性，本研究将观测结果与通过在系统发育树上反复模拟随机羽色反光率演化所得到的效应零分布进行对比。在物种与群落两个水平上，研究均发现：体色更深的鸟类分布于更湿润、更寒冷的区域，以及植被更茂密的生境中。模拟分析验证了物种水平的结果，以及温度在群落水平的效应，但群落水平的降雨量与植被效应落在模拟效应的分布区间内，需谨慎解读。澳大利亚鸟类的种间羽色变异支持格洛杰法则中关于降雨量/植被的预测，但在温度维度上呈现相反的模式。湿润且植被茂密的环境中体色更深的现象，既符合黑色素沉着可防止细菌降解羽毛的作用机制，也与伪装的背景匹配假说一致。若羽色影响体温调节，那么深色羽色在寒冷区域可能具有适应性优势，而在温暖区域则可能产生不利影响——体温调节的选择压力通常仅被认为对变温动物至关重要。本研究数据表明，有必要在不同层级与大尺度范围内检验生物地理学法则的普适性。未来需开展实验研究，以确认羽色非彩色变异与气候之间关联的内在机制。