Data from: Dispersal and the transition to sympatry in vertebrates

Under allopatric speciation models, a key step in the build-up of species richness is population dispersal leading to the co-occurrence of previously geographically isolated forms. Despite its central importance for community assembly, the extent to which the transition from spatial segregation (allopatry or parapatry) to coexistence (sympatry) is a predictable process, or alternatively one governed by chance and the vagaries of biogeographic history, remains poorly understood. Here, we use estimated divergence times and current patterns of geographical range overlap among sister species to explore the evolution of sympatry in vertebrates. We show that rates of transition to sympatry vary predictably according to ecology, being faster in marine or strongly dispersive terrestrial clades. This association with organism vagility is robust to the relative frequency of geographical speciation modes and consistent across taxonomic scales and metrics of dispersal ability. These findings reject neutral models of dispersal assembly based simply on evolutionary age and are not predicted by the main alternative view that range overlap is primarily constrained by biotic interactions. We conclude that species differences in dispersal limitation are fundamental in organizing the assembly of ecological communities and shaping broad-scale patterns of biodiversity over space and time.

在异域物种形成（allopatric speciation）模型中，物种丰富度积累的核心步骤为种群扩散，即此前地理隔离的类群得以实现同域分布。尽管该过程对群落组装具有关键意义，但从空间隔离（异域或邻域分布（parapatry））向同域共存（sympatry）的转变究竟是可预测的演化过程，抑或是由随机性与生物地理历史的变幻莫测所主导，目前仍鲜有研究阐明。

本研究借助姊妹物种（sister species）的估算分化时间与当前地理分布重叠格局，探究脊椎动物的同域演化规律。研究发现，向同域分布的转变速率可依据生态特征进行预测：海洋类群或扩散能力极强的陆生演化支（clades），其转变速率更快。这一与生物扩散能力相关的关联，不受地理物种形成模式相对频率的影响，且在不同分类学尺度与扩散能力度量标准下均保持一致。

上述研究结果驳斥了仅基于演化年龄提出的扩散组装中性模型，且与“分布重叠主要受生物相互作用（biotic interactions）约束”的主流替代观点不符。我们由此认为，物种间的扩散限制差异，是调控生态群落组装、塑造时空尺度上生物多样性宏观格局的核心基础。