Quantifying the role of intra-specific trait variation for allocation and organ-level traits in tropical seedling communities

Questions: Community structure is the outcome of individual-level interactions. Recent work has shown that disaggregating trait information from the species to the individual level can elucidate ecological processes. We aim to integrate trait dispersion analyses across different aggregation levels including a broad range of traits that allow assessment of patterns of variation among co-occurring and non-co-occurring individuals. We ask the following questions: (1) what is the role of intra- and inter-specific dissimilarity within neighbourhoods vs. across neighbourhoods in promoting trait dispersion; (2) how is trait variation partitioned across all individuals in each study system; and (3) are the results consistent across traits and forests? Location: Puerto Rico and China. Methods: We measured allocation and organ-level (e.g. specific leaf area) traits on every individual in two seedling censuses in two tropical rain forests. Then, we partitioned trait variation within and across species, considering its impact on patterns of trait dispersion, and quantifying how these outcomes vary depending on whether allocation-related or organ-level traits are considered. Results: We found an increase in trait dispersion when individual-level traits are considered, reflecting conspecific differentiation for allocation of traits. Organ-level traits, however, do not necessarily promote strong phenotypic displacement within conspecifics. Consistent with this, we found that the majority of variation in allocation of traits was between conspecifics, while most of the variation in organ-level traits was found between species. Conclusions: Overall, trait displacement occurs within and across neighbourhoods, reflecting differentiation at inter- and intra-specific levels. Also, we identify two major phenotypic groups of variation, allocation and organ-level traits, that constitute two contrasting strategies for response to biotic and abiotic contexts: one highlights ecological differences among individuals, while the other highlights differences among species.