Data from: The impact of geographic range, sampling, ecology, and time on extinction risk in the volatile clade Graptoloida

Although extinction risk has been found to have a consistent negative relationship with geographic range across wide temporal and taxonomic scales, the effect has been difficult to disentangle from factors such as sampling, ecological niche, or clade. In addition, studies of extinction risk have focused on benthic invertebrates with less work on planktic taxa. We employed a global set of 1114 planktic graptolite species from the Ordovician to lower Devonian to analyze the predictive power of species’ traits and abiotic factors on extinction risk combining general linear models, partial least squares regression, and permutation tests. Factors included measures of geographic range, sampling and graptolite-specific factors such as clade, biofacies affiliation, shallow water tolerance, and age cohorts split at the base of the Katian and Rhuddanian stages. The percent variance in durations explained varied substantially between taxon subsets from 12-45%. Overall commonness, the correlated effects of geographic range and sampling, was the strongest most consistent factor (12-30% variance explained) with clade and age cohort adding up to 18% and other factors <10%. Surprisingly, geographic range alone contributed little explanatory power (<5%). It is likely that this is a consequence of a non-linear relationship between geographic range and extinction risk where the largest reductions in extinction risk are gained from moderate expansion of small geographic ranges. Thus, even large differences in range size between graptolite species did not lead to a proportionate difference in extinction risk because of the large average ranges of these species. Finally, we emphasize that the common practice of determining the geographic range of taxa from the union of all occurrences over their duration poses a substantial risk of overestimating the geographic scope of the realized ecological niche and, thus, of further conflating sampling effects on observed duration with the biological effects of range size on extinction risk.

尽管已有研究表明，在广泛的时间尺度与分类学尺度下，灭绝风险与地理分布范围之间始终呈负相关关系，但该效应很难与采样偏差、生态位（ecological niche）、演化支（clade）等因素区分开来。此外，现有灭绝风险相关研究多聚焦于底栖无脊椎动物，对浮游类群（planktic taxa）的探讨相对较少。本研究收集了奥陶纪至早泥盆世的1114种全球浮游笔石（planktic graptolite）数据集，结合广义线性模型（general linear models）、偏最小二乘回归（partial least squares regression）以及置换检验（permutation tests），分析物种性状与非生物因子对灭绝风险的预测能力。所纳入的分析因子包括地理分布范围的测算指标、采样强度相关指标，以及笔石专属因子如演化支（clade）、生物相（biofacies）归属、浅水环境耐受性，以及以凯迪阶（Katian）和鲁丹阶（Rhuddanian）底界划分的年龄群（age cohorts）。不同分类群子集的物种存续时间方差解释率存在显著差异，区间为12%至45%。总体而言，由地理分布范围与采样效应共同介导的物种普遍度是解释力最强且最稳定的因子，其方差解释率达12%至30%；演化支与年龄群的联合贡献可达18%，其余因子的解释率均低于10%。令人意外的是，仅地理分布范围单一因子的解释力极低（不足5%）。这一现象大概率源于地理分布范围与灭绝风险之间存在非线性关系：当小型分布范围适度扩张时，灭绝风险的降幅最为显著。因此，由于本研究涉及的笔石物种平均分布范围本就较大，即便不同物种间的分布范围差异显著，也不会对应产生成比例的灭绝风险差异。最后，本研究强调，当前学界通用的“基于物种存续期内所有发现记录的并集来确定类群地理分布范围”的做法，存在严重高估类群实际生态位地理范围的风险，进而会进一步混淆采样效应对观测存续时长的影响，与分布范围大小对灭绝风险的生物学效应。