Data from: Inter-specific functional convergence and divergence and intra-specific negative density dependence underlie the seed-to-seedling transition in tropical trees

The seed-to-seedling transition constitutes a critical bottleneck in the life history of plants and represents a major determinant of species composition and abundance. However, we have surprisingly little knowledge regarding the forces driving this ontogenetic transition. Here we utilize information regarding organismal function to investigate the strength of intra- and inter-specific negative density dependence during the seed-to-seedling transition in Puerto Rican tree species. Our analyses were implemented at individual sites and across an entire 16-ha forest plot, spanning six years. The functional richness of seedling assemblages was significantly lower than expected given the seed assemblages, but the functional evenness is significantly higher than expected indicating the simultaneous importance of constraints on the overall phenotypic space and trait differences for successful transitions from seed to seedling. The results were consistent across years. Within species, we also found evidence for strong intra-specific negative density dependence where the probability of transition was proportionally lower when in a site with high conspecific density. These results suggest that filtering of similar phenotypes across species and strong negative density dependence within and among species are simultaneously driving the structure and dynamics of tropical tree assemblages during this critical life-history transition.

种子到幼苗的转变是植物生活史中的关键瓶颈环节，同时也是决定物种组成与丰度的核心因素。然而，我们对驱动这一个体发育转变的影响因素却知之甚少，这一点颇为出人意料。本研究借助生物功能相关信息，针对波多黎各树种在种子至幼苗转变阶段的种内与种间负密度依赖强度展开探究。我们的分析分别在单个样地以及整片16公顷的森林样地中开展，研究周期跨越6年。相较于初始种子集合，幼苗集合的功能丰富度显著低于预期，但其功能均匀度却显著高于预期——这表明，在种子成功转变为幼苗的过程中，对整体表型空间的限制与性状差异的筛选作用同等重要。上述研究结果在各年份均保持一致。在物种内部层面，我们同样发现了显著的种内负密度依赖证据：当样地内同种个体密度较高时，种子向幼苗转变的概率会成比例降低。上述结果表明，跨物种的相似表型筛选作用，以及种内与种间强烈的负密度依赖，共同驱动了热带树木群落集合在这一关键生活史转变阶段的结构与动态变化。