Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

A variety of ecological processes influence diversity and species composition in natural communities. Most of these processes, whether abiotic or biotic, differentially filter individuals from birth to death, thereby altering species’ relative abundances. Nonrandom outcomes could accrue throughout ontogeny, or the processes that generate them could be particularly influential at certain stages. One long-standing paradigm in tropical forest ecology holds that patterns of relative abundance among mature trees are largely set by processes operating at the earliest life cycle stages. Several studies confirm filtering processes at some stages, but the longevity of large trees makes a rigorous comparison across size classes impossible without long-term demographic data. Here, we use one of the world’s longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and mo...多种生态过程会影响自然群落的生物多样性与物种组成。其中绝大多数过程，无论非生物（abiotic）还是生物（biotic）因子，均会在个体从出生至死亡的完整生命周期内对其实施差异化过滤，进而改变各物种的相对丰度。非随机的群落动态结果既可能贯穿个体发育全程，也可能由特定生命阶段的作用过程主导。热带森林生态学领域存在一项长期沿用的经典范式：成熟林木间的相对丰度格局，在很大程度上由生命周期最早阶段的作用过程所塑造。目前已有多项研究证实了部分生命阶段存在的过滤效应，但大型林木的超长寿命意味着，若缺乏长期种群动态数据（demographic data），便无法对不同径级（size classes）的非随机结果开展严谨对比。本研究依托全球持续运行时间最久的基于样地的森林动态监测项目之一，对不同径级的非随机结果展开对比分析。我们选取了1971年仍存活的186个物种、共计7977个个体组成的同生群（cohort）作为研究对象，并