Data from: Local and global abundance associated with extinction risk in late Paleozoic and early Mesozoic gastropods

Ecological theory predicts an inverse association between population size and extinction risk, but most previous paleontological studies have not confirmed this relationship. The reasons for this discrepancy between theory and observation remain poorly understood. In this study, we compiled a global database of gastropod occurrences and collection-level abundances spanning the Early Permian through Early Jurassic (Pliensbachian). Globally, the database contains 5469 occurrences of 496 genera and 2156 species from 839 localities. Within the database, 30 collections distributed across 7 stages contain at least 75 specimens and 10 genera – our minimum criteria for within-collection analysis of extinction selectivity. We use logistic regression analysis to assess the relationship between abundance and extinction risk using global and local measures of population size and stage-level extinction patterns in Early Permian through Early Jurassic marine gastropods. We find that global genus occurrence frequency is inversely associated with extinction risk (i.e., positively associated with survival) in 15 of 16 stages examined, statistically significantly so in 6 stages. Although correlation between geographic range and occurrence frequency may account for some of this association, results from multivariable regression analysis suggest that the association between occurrence frequency and extinction risk is largely independent of geographic range. Within local assemblages, abundance (number of individuals) is also inversely associated with extinction risk. The strength of association is consistent across time and modes of fossil preservation. Effect strength is poorly constrained, particularly in analyses of local collections. In addition to limited power due to small sample size, this poor constraint may result from confounding by ecological variables not controlled for in the analyses, by taphonomic or collection biases, or from non-monotonic relationships between abundance and extinction risk. Two factors are likely to account for the difference between our results and those of most previous studies. First, many previous studies focused on the end-Cretaceous mass extinction event; the extent to which these results can be generalized to other intervals remains unclear. Second, previous findings of non-selective extinction could result from insufficient statistical power rather than the absence of an underlying effect because non-selective extinction is generally used as the null hypothesis for statistical convenience. Survivorship patterns in late Paleozoic and early Mesozoic gastropods suggest that abundance has been a more important influence on extinction risk through the Phanerozoic than previously appreciated.

生态学理论预言，种群规模与灭绝风险之间存在负相关关系，但此前绝大多数古生物学研究均未验证这一关系。理论与观测结果间的这一矛盾，其成因迄今仍未得到充分阐释。本研究构建了一套覆盖早二叠世至早侏罗世（普林斯巴阶）的全球腹足类（gastropod）产出记录与采集层丰度数据库。该数据库全球范围内共收录839个化石产地的496个属、2156个物种，总计5469条产出记录。数据库中，分布于7个地质阶的30个采集层满足至少75件标本与10个属的最低标准——此为层内灭绝选择性分析的阈值条件。本研究以早二叠世至早侏罗世海洋腹足类为研究对象，采用逻辑回归分析，结合种群规模的全球与局域测度指标以及阶级灭绝模式，探究丰度与灭绝风险之间的关联。研究结果显示，在被考察的16个地质阶中，有15个阶的全球属级产出频率与灭绝风险呈负相关（即与物种存活率呈正相关），其中6个阶的相关性具有统计学显著性。尽管地理分布范围与产出频率之间的相关性或许可以解释部分关联，但多元回归分析结果表明，产出频率与灭绝风险的关联在很大程度上独立于地理分布范围。在局域化石组合中，个体丰度同样与灭绝风险呈负相关。该关联的强度在不同地质时代与化石保存模式下均保持一致。但关联强度的约束性较弱，尤其是在局域采集层的分析中。除样本量偏小导致统计效力不足外，约束性较弱的成因还可能包括：分析中未控制的生态变量带来的混淆效应、埋藏学或采集偏差，或是丰度与灭绝风险间存在非单调的关联关系。有两个因素或可解释本研究结果与多数既往研究的分歧：其一，既往多数研究聚焦于白垩纪末大灭绝事件，此类研究结果能否推广至其他地质时段尚不明晰；其二，既往报道的非选择性灭绝结论，可能源于统计效力不足而非真实不存在该效应——这是因为为方便开展统计检验，研究者通常将非选择性灭绝作为原假设。晚古生代至早中生代腹足类的存活模式表明，在整个显生宙（Phanerozoic）中，丰度对灭绝风险的影响比此前学界认知的更为显著。