Species Traits Mediate Environmental Responses but Not Conspecific Density Dependence in Tropical Tree Saplings

AbstractUnderstanding how functional traits mediate species-specific responses to environmental variation and neighborhood interaction is fundamental for linking individual performance to community assembly. We used a hierarchical framework to examine how functional traits along the acquisitive-conservative spectrum mediate growth responses to environmental effects and density dependence. We monitored the growth of 16,717 saplings from 115 tree species over 5 years in a tropical rainforest and measured 10 functional traits reflecting the acquisitive-conservative spectrum. We employed Bayesian hierarchical models to quantify the relative importance of environmental and density factors on sapling growth and investigate how functional traits mediate species-specific responses to these factors. Sapling growth rates were primarily influenced by soil conditions, light availability (canopy closure), and conspecific adult neighbor density. Acquisitive species exhibited enhanced growth under high light, favorable soil resources, and low aluminum conditions compared with conservative species. However, we found no significant relationship between functional traits and conspecific density dependence. Functional traits mediate environmental responses through divergent resource use strategies rather than conspecific density dependence. Trait-based mechanisms underlying species coexistence may operate through pathways beyond the acquisitive-conservative spectrum. Our hierarchical modeling provides a framework for disentangling the complex relationships between functional traits, environmental responses, and density dependence in diverse tropical forests.