Individual-level trait variation and negative density dependence affect growth in tropical tree seedlings

摘要

Individual-level interactions with neighbours and their surrounding environments are key factors influencing performance that ultimately shape and maintain diversity in tropical plant communities. Theory predicts that the strength of these interactions depends on the similarity among neighbours, the turnover in composition caused by individuals that enter as new recruits and individuals that die, and fitting to local conditions. Despite considerable phenotypic variation among individuals and high community dynamics, these three factors have rarely been considered together for understanding growth variation, especially for seedling communities in the tropics. We address this outstanding challenge by quantifying the influence of trait dissimilarity among neighbours, temporal turnover in neighbours, and individual trait variation on seedling growth, based on an unprecedented dataset containing individual-level demographic and functional trait data for tropical tree seedlings. The results showed that trait dissimilarity associated with resource acquisition does not influence growth. However, conspecific negative density-dependent effects on growth were evident through the initial density of conspecifics and the increase in conspecifics during the study period. Also, individuals with relatively larger investments in leaf biomass allocation attained higher growth rates, suggesting that seedlings adjust their resource allocation to tissues related with light capture.Synthesis. Together, these findings indicate that tropical seedling communities are structured by local abiotic factors that ultimately result in individual variation in resource acquisition traits and by biotic interactions driven by negative density dependence. These biotic interactions are highly dynamic and depend on conspecifics turnover, even at short temporal scales. Thus, to gain further insights into the forces structuring seedling communities, future studies should account for temporal variability in immediate neighbours and individual-level phenotypic variation that influence individual interactions.