Strong relationships between morphological and ecological characters are commonly predicted to reflect the association between form and function, with this hypothesis being well supported in restricted taxonomic and geographic contexts. Conversely, among broader sets of species, ecological variables have been shown to have limited power to explain morphological variation. To understand these apparent discrepancies, for a large and globally distributed passerine radiation we test (i) whether the character states of four ecological variables (foraging mode, diet, strata and habitat) have different morphological optima, (ii) whether ecological variables explain substantial variance in morphology, and (iii) whether ecological character states can be accurately predicted from morphology. We collected ten linear morphological measurements for 782 species of corvoid passerines, and assessed (i) the fit of models of continuous trait evolution with different morphological optima for each ecological character state, (ii) variation in morphological traits among ecological character states using phylogenetically corrected regressions, and (iii) the accuracy of morphological traits in predicting species-level membership of ecological character states using linear discriminant analysis (LDA). Models of morphological evolution with different ecological optima were well supported across numerous morphological axes, corresponding with significant differences in trait distributions among ecological character states. LDA also showed that membership of the ecological categories can be predicted with relatively high accuracy by morphology. In contrast to these findings, ecological variables explain limited amounts of variation in morphological traits. For a global radiation of passerine birds, we confirm that the generation of morphological variation is generally consistent with ecological selection pressures, but that ecological characters are of limited utility in explaining morphological differences among species. Although selection towards different optima means that membership of ecological character states tend to be well predicted by morphology, the overall morphospace of individual ecological character states tend to be broad, implying that morphology can evolve in multiple ways in response to similar selection pressures. Extensive variation in morphological adaptations among similar ecological strategies is likely to be a widespread phenomenon across the tree of life.

中文翻译：

---

全球燕雀辐射形态和生态特征之间的关联

形态特征和生态特征之间的强关系通常被预测为反映形式和功能之间的关联，这一假设在有限的分类学和地理背景下得到了很好的支持。相反，在更广泛的物种中，生态变量已被证明对解释形态变化的能力有限。为了理解这些明显的差异，对于一个大型的全球分布的燕雀类辐射，我们测试（i）四个生态变量（觅食模式、饮食、地层和栖息地）的特征状态是否具有不同的形态优化，（ii）生态变量是否解释了实质性的形态的差异，以及（iii）是否可以从形态准确预测生态特征状态。我们收集了 782 种燕雀科动物的 10 个线性形态测量结果，并评估了（i）每个生态特征状态具有不同形态最优值的连续性状进化模型的拟合，（ii）使用系统发育校正的生态特征状态之间形态特征的变化回归，以及 (iii) 形态特征在使用线性判别分析 (LDA) 预测生态特征状态的物种级成员资格方面的准确性。具有不同生态最优的形态演化模型在众多形态轴上得到了很好的支持，对应于生态特征状态之间性状分布的显着差异。LDA 还表明，可以通过形态学以相对较高的精度预测生态类别的成员资格。与这些发现相反，生态变量解释了形态特征的有限变化。对于雀鸟的全球辐射，我们证实形态变异的产生通常与生态选择压力一致，但生态特征在解释物种间形态差异方面的效用有限。尽管对不同最优值的选择意味着生态特征状态的成员资格往往可以通过形态学很好地预测，但个体生态特征状态的整体形态空间往往很宽，这意味着形态可以以多种方式进化以响应相似的选择压力。相似生态策略之间形态适应性的广泛变化可能是整个生命之树的普遍现象。