Data from: The association between morphological and ecological characters across a global passerine radiation

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.

形态性状与生态性状间的强关联通常被推测反映了形态与功能之间的联系，该假说在有限的分类学和地理情境中得到了充分验证。与之相反，在更大范围的物种类群中，生态变量被证实对解释形态变异的解释力有限。为厘清这些看似矛盾的现象，针对一个体型庞大且全球分布的雀形目辐射演化类群，我们开展了三项检验：（1）四项生态变量（觅食方式、食性、栖息层和栖息地）的性状状态是否对应不同的形态最适值；（2）生态变量是否能够解释形态学上的显著变异；（3）能否通过形态学特征准确预测生态性状状态。我们采集了782种鸦总科雀形目鸟类的10项线性形态学测量数据，并开展了三项评估：（1）针对各生态性状状态，拟合具有不同形态最适值的连续性状演化模型，评估其适配度；（2）通过系统发育校正回归分析，比较不同生态性状状态间的形态性状差异；（3）借助线性判别分析（Linear Discriminant Analysis, LDA），评估利用形态性状预测物种所属生态性状类别的准确率。具有不同生态最适值的形态演化模型在多个形态学维度上均得到了良好支持，这与不同生态性状状态间的性状分布存在显著差异的结果一致。线性判别分析结果同样显示，通过形态特征能够以较高准确率预测物种所属的生态类别。但与上述结果相悖的是，生态变量对形态性状变异的解释力度仍较为有限。针对全球分布的雀形目鸟类辐射类群，本研究证实：形态变异的产生通常与生态选择压力相符，但生态性状在解释物种间形态差异方面的实用性有限。尽管针对不同最适值的选择使得生态性状状态的归属可通过形态特征较好地预测，但单一生态性状状态的整体形态空间往往较为宽泛，这意味着在相似选择压力下，形态可通过多种路径演化。相似生态策略下形态适应的广泛变异，可能是生命之树中普遍存在的现象。