Data from: Abundance inequality in freshwater communities has an ecological origin

The hollow-shaped species abundance distribution (SAD) and its allied rank abundance distribution (RAD)—showing that abundance is unevenly distributed among species—are some of the most studied patterns in ecology. To explain the nature of abundance inequality, I developed a novel framework identifying environmental favorability, which controls the balance between reproduction and immigration, as the ultimate source and species stress tolerance as a proximate factor. Thus, under harsh conditions, only a few tolerant species can reproduce, while some sensitive species can be present in low numbers due to chance immigration. This would lead to high abundance inequality between the two groups of species. Under benign conditions, both groups can reproduce and give rise to higher abundance equality. To test these ideas, I examined the variability in the parameters of a Poisson lognormal fit of the SAD and a square root fit of the RAD in diatom and fish communities across US streams. Indeed, as environmental favorability increased, more sensitive forms were able to establish large populations, diminishing the abundance disparity between locally common and rare species. Finally, it was demonstrated that in diatoms, the RAD belonged to the same family of relationships as those of population density with body size and regional distribution.

中空型物种多度分布（Species Abundance Distribution, SAD）及其关联的等级多度分布（Rank Abundance Distribution, RAD）——该分布揭示了物种间多度分布不均的普遍现象——是生态学领域被研究最为广泛的群落格局之一。为阐释物种多度不均的本质，本文构建了一套全新的理论框架：将调控繁殖与迁入平衡的环境适宜度作为多度不均的根本来源，将物种胁迫耐受性作为其近因调控因素。据此框架，在严苛环境条件下，仅少数耐受型物种能够完成繁殖过程，而部分敏感物种仅可通过偶然迁入以极低多度存在，这将显著拉大两类物种间的多度差异；在环境适宜的条件下，两类物种均可完成繁殖，进而提升群落内多度分布的均匀性。为验证上述假说，本文针对美国溪流中的硅藻群落与鱼类群落，分别对SAD进行泊松对数正态拟合、对RAD进行平方根拟合，并分析两类拟合参数的变异性。研究结果证实，随着环境适宜度的提升，更多敏感物种得以建立大规模种群，从而缩小了本地常见种与稀有种之间的多度差异。此外，本研究还证实，在硅藻类群中，RAD所遵循的关系模式，与种群密度、个体大小及区域分布间的关联模式同属一类关系族。