Data from: Gauging scale effects and biogeographical signals in similarity distance decay analyses: an Early Jurassic ammonite case study

In biogeography, the similarity distance decay (SDD) relationship refers to the decrease in compositional similarity between communities with geographical distance. Although representing one of the most widely used relationships in biogeography, a review of the literature reveals that: (1) SDD is influenced by both spatial extent and sample size; (2) the potential effect of the phylogenetic level has yet to be tested; (3) the effect of a marked biogeographical structuring upon SDD patterns is largely unknown; and (4) the SDD relationship is usually explored with modern, mainly terrestrial organisms, whereas fossil taxa are seldom used in that perspective. Using this relationship, we explore the long-distance dispersal of the Early Jurassic (early Pliensbachian, c. 190.8 Ma to 187.6 Ma) ammonites of the western Tethys and adjacent areas, in a context of marked provincialism. We show that the long-distance dispersal of these ammonites is not related to shell size and shape, but rather to the environmental characteristics of the province to which they belong. This suggests that their long-distance dispersal may have been essentially driven by passive planktonic drift during early juvenile, post-hatching stages. Furthermore, it seems that the SDD relationship is not always an appropriate method to characterize the existence of a biogeographical structuring. We conducted SDD analyses at various spatial, sampling and phylogenetic scales in order to evaluate their sensitivity to scale effects. This multi-scale approach indicates that the sampling scale may influence SDD rates in an unpredictable way and that the phylogenetic level has a major impact on SDD patterns.在生物地理学领域，距离衰减相似性（similarity distance decay, SDD）关系指不同群落间的组成相似性随地理距离增加而降低的现象。尽管该关系是生物地理学中应用最为广泛的研究范式之一，但现有文献综述显示：（1）SDD同时受空间范围与样本量的双重影响；（2）系统发育层级的潜在效应尚未得到实证检验；（3）显著生物地理结构对SDD格局的影响仍基本未被探明；（4）当前SDD关系的研究多聚焦于现代陆生生物，极少有研究从该视角探讨化石类群。依托该关系，本研究针对特提斯洋西部及毗邻区域早侏罗世（普林斯巴阶早期，约190.8 Ma至187.6 Ma）的菊石展开长距离扩散研究，研究背景为显著的生物地理分区性。研究结果表明，这些菊石的长距离扩散与壳体大小和形态无关，而是与其所属生物地理分区的环境特征紧密相关。这暗示其长距离扩散可能主要由孵化后的幼体早期阶段的被动浮游漂流所驱动。此外，本研究同时发现，SDD关系并非总能作为表征生物地理结构存在性的适宜方法。为评估不同尺度下SDD分析对尺度效应的敏感性，我们在不同空间、采样及系统发育尺度下开展了SDD分析。该多尺度分析表明，采样尺度可能以不可预测的方式影响SDD速率，而系统发育层级则对SDD格局具有显著影响。