Data from: Repeated parallel evolution reveals limiting similarity in subterranean diving beetles

The theory of limiting similarity predicts that co-occurring species must be sufficiently different to coexist. Although this idea is a staple of community ecology, convincing empirical evidence has been scarce. Here we examine 34 subterranean beetle communities in arid inland Australia that share the same habitat type but have evolved in complete isolation over the past 5 million years. Although these communities come from a range of phylogenetic origins, we find that they have almost invariably evolved to share a similar size structure. The relative positions of coexisting species on the body size axis were significantly more regular across communities than would be expected by chance, with a size ratio, on average, of 1.6 between coexisting species. By contrast, species’ absolute body sizes varied substantially from one community to the next. This suggests that self-organized spacing according to limiting-similarity theory, as opposed to evolution toward preexisting fixed niches, shaped the communities. Using a model starting from random sets of founder species, we demonstrate that the patterns are indeed consistent with evolutionary self-organization. For less isolated habitats, the same model predicts the coexistence of multiple species in each regularly spaced functional group. Limiting similarity, therefore, may also be compatible with the coexistence of many redundant species.

极限相似性理论（limiting similarity）预测，同域共存的物种必须具备足够的差异方可实现共存。尽管这一观点是群落生态学的核心经典观点之一，但与之对应的可靠实证证据却长期匮乏。本研究聚焦澳大利亚内陆干旱区域的34个地下甲虫群落，这些群落虽共享相同的生境类型，但在过去500万年中始终处于完全隔离的演化状态。尽管这些群落的系统发育起源各异，但我们发现它们几乎无一例外地演化出了相似的体型结构。共存物种在体型轴上的相对位置在不同群落间呈现出显著的规律性，远高于随机预期的结果，共存物种间的平均体型比约为1.6。与之相对，不同群落中物种的绝对体型差异则十分显著。这表明，塑造这些群落的并非向预先存在的固定生态位演化的过程，而是符合极限相似性理论的自组织空间分布模式。我们以随机奠基者物种集合为起点构建模型，证实该群落格局确实符合演化自组织的规律。对于隔离程度较低的生境，同一模型可预测每个规则分布的功能群中均可共存多个物种。因此，极限相似性理论同样可以解释诸多冗余物种的共存现象。