Data from: Demographic properties shape tree size distribution in a Malaysian rain forest

Different mechanisms have been proposed to explain how vertical and horizontal heterogeneity in light conditions enhances tree species coexistence in forest ecosystems. The foliage partitioning theory proposes that differentiation in vertical foliage distribution, caused by an interspecific variation in mortality-to-growth ratio, promotes stable coexistence. In contrast, successional niche theory posits that horizontal light heterogeneity, caused by gap dynamics, enhances species coexistence through an interspecific trade-off between growth rate and survival. To distinguish between these theories of species coexistence, we analyzed tree inventory data for 370 species from the 50-ha plot in Pasoh Forest Reserve, Malaysia. We used community-wide Bayesian models to quantify size-dependent growth rate and mortality of every species. We compared the observed size distributions and the projected distributions from size-dependent demographic rates. We found that the observed size distributions were not simply correlated with the rate of population increase but were related to demographic properties such as size growth rate and mortality. Species with low relative abundance of juveniles in size distribution showed high growth rate and low mortality at small tree sizes and low per-capita recruitment rate. Overall, our findings were in accordance with those predicted by foliage partitioning theory.

已有多种机制被提出，用以阐释森林生态系统中光照条件的垂直与水平异质性如何促进树种共存。叶片分层理论（foliage partitioning theory）指出，由种间死亡率-生长率比差异所引发的垂直叶片分布分化，可推动物种实现稳定共存。与之相对，演替生态位理论（successional niche theory）则提出，由林隙动态（gap dynamics）导致的水平光照异质性，可通过生长率与存活之间的种间权衡增强物种共存能力。为区分这些物种共存理论，我们分析了取自马来西亚巴索森林保护区（Pasoh Forest Reserve）50公顷样地的370个物种的林木清查数据。我们运用群落级贝叶斯模型（Bayesian model）量化了各物种的体型依赖型生长率与死亡率。我们将实测得到的体型分布，与基于体型依赖型种群动态速率预测得到的分布进行了对比。研究结果表明，观测到的体型分布并非仅与种群增长率相关，而是与体型生长率、死亡率等种群动态属性紧密相关。在体型分布中幼树相对丰度较低的物种，其小型个体的生长率较高、死亡率较低，且单位个体补充率偏低。总体而言，我们的研究发现与叶片分层理论的预测结果一致。