Species assembly and coexistence mediated by phylogenetic and functional diversities: an experimental perspective in plant communities of semiarid gypsum systems

Abstract

Understanding the assembly process and species coexistence forming a community are still one of the main objectives of community ecology. The different theories and approaches trying to explain these processes have evolved over the years. From an early approach in which it was considered that only certain combinations of species could occur in nature, to the idea that communities are simply a coincidence of species, where arrival of propagules and ecological drift play a major role. All these approaches have generated interesting debates over time, reaching the most recent one between Niche Theory and Neutrality Theory. Nowadays, the scientific community is moving towards an integration of both processes (stochastic and deterministic), understanding that both play a decisive role in the formation of communities. Although both approaches have received much attention, most studies have based mainly on observational studies due to the difficulty of manipulating whole communities. However, further progress in understanding the assembly rules and coexistence mechanisms involved in community formation requires an experimental approach, feasible by manipulating the functional and phylogenetic properties of the community, in combination with the abiotic and biotic factors operating during the assembly process, to unequivocally establish cause-effect relationships. Moreover, the fundamental tools available to study the community not only taxonomically, but also functionally and phylogenetically, have now been greatly refined. Functional diversity provides information on the filtering effects of environmental factors present in a system, while phylogenetic diversity summarises morphological, physiological and phenological characteristics throughout the evolution of species. Therefore, with this thesis we aim to explore the mechanisms of species assemblage and coexistence in the context of niche and neutrality theories through an experimental approach, manipulating the functional and phylogenetic diversity of complete assemblages via common garden experiments in greenhouses with annual plants, as well as the environmental filters operating on natural assemblages via field experiments.