Data from: Relationships of diversity, disparity and their evolutionary rates in squirrels (Sciuridae)

Several theories predict that rapidly diversifying clades will also rapidly diverge phenotypically; yet, there are also reasons for suspecting that diversification and divergence might not be correlated. In the widely distributed squirrel clade (Sciuridae), we test for correlations between per-lineage speciation rates, species richness, disparity and a time-invariant measure of disparity that allows for comparing rates when evolutionary modes differ, as they do in squirrels. We find that species richness and speciation rates are not correlated with clade age or with each other. Disparity appears to be positively correlated with clade age because young, rapidly diversifying Nearctic grassland clades are strongly pulled to a single stable optimum but older, slowly diversifying Paleotropical forest clades contain lineages that diverge along multiple ecological and morphological lines. That contrast is likely due to both the environments they inhabit and their phylogenetic community structure. Our results argue against a shared explanation for diversity and disparity in favor of geographically mediated modes of speciation and ecologically mediated modes of phenotypic evolution.

多项理论预测，快速辐射演化的支系（clade）也会在表型层面快速分化；然而，也有诸多理由让人怀疑物种辐射演化与表型分化之间未必存在关联。在分布广泛的松鼠科（Sciuridae）支系中，我们针对支系水平的物种形成速率、物种丰富度、表型差异度（Disparity）以及一种不随时间变化的表型差异度测算方法展开相关性检验——该方法可在演化模式存在差异（正如松鼠类群的情况）的前提下对演化速率进行比较。我们的研究结果显示，物种丰富度与物种形成速率既不与支系年龄相关，彼此之间也不存在相关性。表型差异度似乎与支系年龄呈正相关，这是因为年轻且快速辐射演化的新北区草原支系会被强烈拉向单一的稳定最优表型；而年代更久远、演化速率较慢的古热带森林支系，其内部支系会沿着多条生态与形态维度发生分化。这种差异大概率与其所处的栖息环境以及系统发育群落结构均有关联。我们的研究结果不支持“物种多样性与表型差异度共享同一演化解释框架”的观点，转而支持“物种形成模式受地理因素介导、表型演化模式受生态因素介导”的结论。