The Role of Deterministic and Stochastic Processes During the Assembly of Tropical Plant Communities through the Lens of Functional Groups

Understanding the processes maintaining species richness and abundance is a central focus in ecology. This is particularly relevant for highly diverse communities such as tropical forests. Several hypotheses have been proposed to explain the maintenance of many species and forest functionality in a continuum between neutral- and niche-based frameworks. Integrating functional traits into community ecology has improved and refined our interpretability of the main processes assembling plant communities. In particular, niche differentiation by a few key functional groups has been suggested to play an essential role in capturing the emergent patterns observed in tropical forests. However, the integration of functional groups into forest dynamics has not been well explored. In this dissertation, I integrate both neutral and niche frameworks with functional traits, habitat differentiation, conspecific negative density dependence, intraspecific trait variation, and ontogeny to understand the role of these frameworks in promoting diversity in highly diverse tropical forests. In the first chapter, I introduce the overall big picture of this dissertation. In the second chapter, I evaluate the functional group version of the neutral theory of forest dynamics. I show that deterministic processes likely govern forest dynamics at the functional group level where species relative abundances change or drift within groups. In the third chapter, I run process-based simulations to understand the relative role of neutrality, functional groups, and conspecific negative density dependence in predicting forest dynamics. I show that a functional group structure with negative density dependence is necessary to produce realistic species and functional diversity levels. In the last chapter, I investigate the trait variation within and between species in functional groups to assess the role of this variation in driving niche differentiation throughout ontogeny. While the functional group delimitation captures realistic functional patterns, the integration of species differences is critical to understanding their effects on species coexistence. Together, these findings expand our understanding of the consequences of integrating functional groups into community ecology and how these groups govern ecological interactions in tropical forests.