Habitat Filtering Covers the Strength of Density Dependence and Functional Density Dependence on Seedling Survival in Cangshan Mountain, Southwest China

Abstract

Conspecific negative density dependence (CNDD) is an important mechanism for species coexistence and community dynamics. Phylogenetic negative density dependence (PNDD) and functional negative density dependence (FNDD) are extensions of CNDD, and many studies have shown that they have become powerful and reliable methods for exploring the mechanisms of species coexistence. However, most studies have focused on only one or two of these mechanisms and have not considered whether and how habitat variables affect the detection of these density dependences. To investigate the relative importance of these mechanisms, we set up three 0.09 ha dynamic plots at Cangshan Mountain in southwest China, and used generalized linear mixed models to analyze how the survival of 546 woody plant seedlings was affected by neighborhood density and habitat variables. Our results showed that heterospecific seedling density dependence and functional trait density dependence played key roles in seedling survival. Habitat factors, phylogenetic densities, and adult neighbors had no significant effect on seedling survival in the three plots. However, habitat filtering covered the detection of density dependence and functional trait density dependence. Our study demonstrates that failure to control for habitat variables may obscure the importance of density dependence and functional trait density dependence on seedling survival.