Dataset_S5.xlsx from The causes of species richness patterns among clades

Two major types of species richness patterns are spatial (e.g. the latitudinal diversity gradient) and clade-based (e.g. the dominance of angiosperms among plants). Studies have debated whether clade-based richness patterns are explained primarily by larger clades having faster rates of species accumulation (speciation minus extinction over time; diversification-rate hypothesis) or by simply being older (clade-age hypothesis). However, these studies typically compared named clades of the same taxonomic rank, such as phyla and families. This study design is potentially biased against the clade-age hypothesis, since clades of the same rank may be more similar in age than randomly selected clades. Here, we analyse the causes of clade-based richness patterns across the tree of life using a large-scale, time-calibrated, species-level phylogeny and random sampling of clades. We find that within major groups of organisms (animals, plants, fungi, bacteria, archaeans), richness patterns are most strongly related to clade age. Nevertheless, weaker relationships with diversification rates are present in animals and plants. These overall results contrast with similar large-scale analyses across life based on named clades, which showed little effect of clade age on richness. More broadly, these results help support the overall importance of time for explaining diverse types of species richness patterns.

物种丰富度格局主要分为两大类：空间格局（例如纬度多样性梯度）以及基于演化支(clade)的物种丰富度格局（例如植物类群中被子植物的主导地位）。学界围绕基于演化支的物种丰富度格局的成因长期存在争论：一派观点认为，更大的演化支拥有更快的物种积累速率（即长期内物种形成速率减去灭绝速率，又称多样化速率假说(diversification-rate hypothesis)）；另一派观点则认为其成因仅为演化支自身的存续时长更长（即演化支年龄假说(clade-age hypothesis)）。然而，过往相关研究通常仅比较了分类层级相同的命名演化支，例如门(phylum)与科(family)。此类研究设计可能对演化支年龄假说存在偏倚，由于相同分类层级的演化支，其形成时长相较于随机选取的演化支往往更为接近，无法有效剥离演化支年龄与多样化速率的独立影响。本研究依托大规模时间校准的物种级系统发育树，并对演化支进行随机抽样，以此分析全球生命树中基于演化支的物种丰富度格局的成因。研究结果显示，在动物、植物、真菌、细菌、古菌(archaeans)这几大类生物类群中，物种丰富度格局与演化支年龄的相关性最为显著。不过，在动物与植物类群中，物种丰富度格局与多样化速率仍存在较弱的相关性。上述整体结论与此前基于命名演化支开展的同类全球生命树大规模分析结果相悖——后者并未发现演化支年龄对物种丰富度存在显著影响。从更广泛的视角来看，本研究结果进一步佐证了时间在解释各类物种丰富度格局中的核心重要性。