Data from: Accounting for differences in species frequency distributions when calculating beta diversity in the fossil record

1. Beta diversity is a measure of the taxonomic differentiation between habitats/localities within an assemblage, and is normally calculated as a set of pairwise taxonomic “distances” between the localities. 2. Due to the incomplete sampling, beta diversity estimates for fossil assemblages will always be higher than the true value. However, the difference between the observed and true distances will vary greatly depending on differences in the shape of the relative abundance distribution. 3. Using simulations, it is shown that incomplete sampling of a homogenous fauna with more even relative abundances of taxa produces higher beta diversity than one with very few extremely common taxa. 4. A new procedure is proposed for calculating beta diversity in the fossil record, whereby the observed distances are compared to the distance obtained by randomly resampling a homogenous fauna with the same abundance distribution. This procedure is named Relative Abundance Corrected beta diversity (RAC beta diversity). Simulations indicate that this method outperforms raw beta diversity estimates, providing beta diversity estimates closer to the true values even when the assumptions of the method are violated. 5. This method is applied to an empirical dataset: Permian-Triassic tetrapods from the Karoo Supergroup of South Africa. Increased provincialism is found across the Permian-Triassic boundary in contrast to uncorrected beta diversity patterns.

1. β多样性（Beta diversity）是衡量某一化石组合内不同生境或地点间分类学分异程度的指标，通常以各地点之间的成对分类学“距离”集合进行计算。2. 由于采样不完整，化石组合的β多样性估计值始终会高于真实值。不过，观测距离与真实距离之间的差值，会因相对多度分布的形态差异而产生显著变化。3. 模拟实验结果表明，对分类群相对多度更为均匀的同质动物群进行不完整采样时，所得到的β多样性会高于仅存在极少数极优势类群的同质动物群。4. 本研究提出一种用于计算化石记录中β多样性的新方法：将观测得到的分类学距离，与对具有相同多度分布的同质动物群进行随机重采样所得到的距离进行比对。该方法被命名为相对多度校正β多样性（Relative Abundance Corrected beta diversity，简称RAC β多样性）。模拟实验表明，相较于原始β多样性估计方法，此方法性能更优，即便在违反方法假设的情况下，仍能得到更接近真实值的β多样性估计结果。5. 将该方法应用于一组实证数据集：采自南非卡鲁超群的二叠纪-三叠纪四足类化石。与未校正的β多样性模式相反，研究发现在二叠纪-三叠纪界线处，生物群的区域分异程度显著升高。