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）是衡量集合群落内不同生境/采样点间分类学差异的指标，通常通过计算各采样点之间的成对分类学"距离"来获取。2. 由于采样不完整，化石集合群落的β多样性估算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物种相对丰度分布的形态差异而产生显著变化。3. 模拟实验结果表明，相较于类群间仅有极少数物种占据绝对优势的均质动物群，物种相对丰度更为均匀的均质动物群在采样不完整时，其估算得到的β多样性更高。4. 本研究提出一种适用于化石记录的β多样性计算新方法：将观测得到的分类学距离，与基于具有相同丰度分布的均质动物群进行随机重采样所获得的距离进行比对。该方法被命名为相对丰度校正β多样性（Relative Abundance Corrected beta diversity，简称RAC β多样性）。模拟实验结果显示，该方法优于原始β多样性估算方法，即使在方法假设条件被违背的情况下，仍能得到更接近真实值的β多样性估算结果。5. 该方法被应用于一项实证数据集：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多样性模式相比，研究发现二叠纪-三叠纪界线处的区域分异程度显著升高。