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.

空心型物种多度分布（SAD）及其关联的秩多度分布（RAD）——揭示了物种间多度分布不均的特征——是生态学领域研究最为广泛的格局之一。为阐释多度不平等的本质，本文构建了全新的分析框架：将调控繁殖与迁入平衡的环境适宜度作为多度不平等的终极成因，将物种胁迫耐受性作为其近因影响因素。据此，在严苛环境中，仅少数耐受物种可完成繁殖过程，而部分敏感物种仅能通过偶然迁入以低丰度存续，这将导致两类物种间的多度差异显著扩大；在适宜环境下，两类物种均可完成繁殖，进而提升了多度分布的均等性。为验证上述假说，本文分析了美国溪流中硅藻与鱼类群落的SAD泊松对数正态拟合参数，以及RAD平方根拟合参数的变异特征。结果证实，随着环境适宜度提升，更多敏感类群得以建立大型种群，削弱了本地常见种与稀有种间的多度差距。最后，本研究证实，在硅藻类群中，RAD所遵循的关系族与种群密度同个体大小、区域分布的关系族相一致。