Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : How communities influence ecosystem processes : the role of species diversity, functional diversity, and functional identity

Auteur : Mokany, Karel

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD)

Résumé
Many biological communities are currently experiencing rapid changes in their diversity and composition, due largely to the intensification of human impacts on natural ecosystems. Alterations to the structure and diversity of communities have the potential to influence a broad range of ecosystem processes (biogeochemical pools and fluxes) which are of key importance to the integrity of natural systems and the well-being of humans. Consequently, increasing research attention is being given to understand how the diversity and composition of biological communities influences key ecosystem processes. This thesis examined how ecosystem processes are related to a broad range of community attributes, using native grasslands as a study system. I investigated this topic, and associated issues, using a variety of approaches, including conceptual and theoretical explorations, pot based experiments, mechanistic modelling, and a major field study of a native grassland system. Importantly, I applied a functional trait approach to gain a greater understanding of how the functional diversity and composition of communities may influence ecosystem processes. The results presented in this thesis overwhelmingly support Grime’s (1998) mass ratio hypothesis, which proposes that the functional attributes of the dominant species in a community largely determine the effect of the biota on ecosystem processes. In the native grassland system I studied, the functional identities of the dominant species were the most important community attribute influencing the magnitude and variability of ecosystem processes. Functional trait diversity also had significant effects on ecosystem processes, although it was generally found to be weaker than the functional identities of the dominant species in predicting ecosystem processes. Functional trait diversity essentially represents the degree of complementarity between species, or the diversity of ways in which species access and utihse resources. My results suggest that complementarity can be important in influencing ecosystem processes, but in most cases it is not as important as the functional identities of the dominant species. In contrast, ecosystem processes tended to be poorly related to traditional measures of community diversity, such as species richness and functional group richness. These results suggest that major changes in the dominance hierarchies of communities are likely to have the greatest impact on ecosystem processes, with only minor effects expected following the loss of rare species.

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