COS 2-8
Negative functional density dependence and the seed to seedling transition in tropical trees
Negative density dependence (NDD) occurs when conspecifics affect the performance, preventing common species to become locally dominant and favoring species coexistence. Intraspecific NDD has been consistently reported and proposed to explain species diversity in tropical communities, but it is still unknown weather NDD affects the functional similarity among species. In this study we ask do similar functions have a negative density effect on the survival of seedlings across the seed to established seedling transition? If there is a negative functional density dependence process structuring seedling communities, we predict that species exhibiting similar traits will have strong negative effects on species performance leading to a seedling community with high functional diversity. Alternatively, if environmental filtering is more important, species with particular traits will be filtered from the community, leading to a seedling community with small functional volume within which species compete. To determine the influence of these effects on functional diversity we compared the functional diversity of seedlings to the functional diversity of seeds of 120 sites in a moist forest, Puerto Rico. We also compared the changes in species diversity in the seed stage and seedlings stage.
Results/Conclusions
Seedlings exhibit only a small range of the functional diversity of the total functional diversity of seeds in the same site. This pattern is consistent with the second scenario proposed, where only a restricted combination of traits is filtered during the seed to established seedling transition. Although our results did not show that negative density dependent processes have a relevant role shaping the functional diversity, the species diversity comparisons showed contrasting patterns. Slopes of regressions between seed and seedling species diversity were less than 1 for all the species analyzed, suggesting that seedling community is strongly affected by negative density dependence process. Our results suggest that during the early stages of development, plants are submitted to two opposite forces that are occurring at the same time determining the structure the seedling communities. Functional traits are strongly filtered, but within this constrained functional space there is strong intraspecific NDD favoring the prevalence of rare species and co-existences.