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.

尽管已有研究证实，在广泛的时间与分类学尺度下，物种灭绝风险与地理分布范围存在稳定的负相关关系，但该效应很难与采样、生态位（ecological niche）以及支系（clade）等因素区分开来。此外，当前灭绝风险相关研究多聚焦于底栖无脊椎动物，针对浮游类群（planktic taxa）的探讨相对不足。本研究依托奥陶纪至早泥盆世的全球1114种浮游笔石（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）与置换检验（permutation tests），分析物种性状与非生物因子对灭绝风险的预测能力。本次分析涵盖的影响因子包括地理分布范围、采样情况，以及笔石专属因子，如支系（clade）、生物相归属（biofacies affiliation）、浅水耐受性，以及以凯迪阶（Katian）和鲁丹阶（Rhuddanian）底界划分的年龄组群。不同分类群子集所解释的存续期方差占比差异显著，区间为12%至45%。总体而言，“普遍度”——即地理分布范围与采样效应的协同作用——是解释能力最强且最为稳定的影响因子，可解释12%~30%的方差；支系（clade）与年龄组群的贡献合计可达18%，其余因子的解释占比均低于10%。令人意外的是，仅地理分布范围本身的解释能力极低，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的非线性关系：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，尽管笔石物种间的分布范围大小存在显著差异，但由于该类群的平均分布范围本就较大，其灭绝风险并不会随分布范围的变化呈现成比例的差异。最后，本研究强调：学界普遍采用的“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，存在极大的高估物种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期的影响与分布范围大小对灭绝风险的生物学效应。