Intraspecific and phylogenetic density-dependent recruitment in a subtropical evergreen forest
Negative density-dependent (NDD) mortality can promote species coexistence through a spacing mechanism that prevents species from becoming too locally abundant. Recently, both evolutionary theory and empirical results suggest that the negative effect of other plants on a focal plant should be higher for closely related neighbors than for less related neighbors. Using 5-years of community-wide seedling and seed rain data from 130 stations (consisting of one 0.5 m2 seed trap and three adjacent 1 m2seedling plots) in a subtropical evergreen forest, we searched for significant intraspecific and phylogenetic density-dependent recruitment from the seed to seedling stage. For 14 focal species, we modeled the number of seedling recruits as a function of conspecific seed density, heterospecific seed density, and phylogenetic diversity using generalized linear models with binomial errors.
For all 14 species, we found significant negative effects of conspecific seed density on the probability of transition from the seed to seedling stage, indicating that conspecific negative density-dependent recruitment for individual species is pervasive and strong. In contrast, for most species, there was no significant effect of heterospecific seed density on the number of seedlings recruiting. However, the phylogenetic diversity of seeds did have a significant impact on recruitment for the majority of species, suggesting that the seed to seedling transition rate is enhanced by being in a neighborhood where heterospecific seeds are not closely related. Based on previous studies, it is likely that the observed negative effects of both conspecific and closely related seeds on recruitment are due to shared natural enemies, specifically pathogens.
In conclusion, our results suggest both intraspecific and phylogenetic density-dependent seedling recruitment play a role in shaping dynamics and community composition in this subtropical forest.