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

Titre : Resilience and resistance of ephemeral aquatic ecosystems to environmental change

Auteur : Mokany, Allie

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2006

Résumé
Understanding the processes that determine the structure of ecosystems is a central challenge of modem ecology. However, the inherent complexity of ecosystems makes it difficult to determine how changes to the natural abiotic environment can influence feedbacks between biota and ecosystem processes. In this thesis, I examine how the relationships between biodiversity, ecosystem processes and stability change with environmental context, using field-based experimental pond microcosms. I investigated the community structure and ecosystem process (i.e. biogeochemical pools and fluxes) as well as the responses of microcosms to a range of environmental changes. These changes included drought, shade and resource addition, imposed upon ponds that differed in seasonal timings and durations of community assembly. Stability was assessed in terms of resistance and resilience. Results indicated overall that biodiversity and ecosystem processes were not strongly linked in this system, particularly in their responses to disturbance. For example, while both productivity and filamentous algae (metaphyton) abundance were congruent in their responses to drought, generally having low resistance but high resilience, faunal measures had limited response to the imposition of the drought but did respond to its removal. Hence, the stability of biodiversity and ecosystem processes was not well correlated. This notion was further strengthened by an experiment that found a limited response of biodiversity and ecosystem processes to variation in shade. In this experiment, there was stronger correlation between ecosystem processes and specific primary producers and consumers (such as metaphyton, tadpoles and Daphnia) than between ecosystem processes and shade levels or aggregate faunal diversity measures. In subsequent studies I determined that the abundance of metaphyton was the primary determinant of the level of ecosystem processes. However, the strength of these relationships varied depending on the abundances of resources, timing of colonization by key invertebrates and presence of competing consumers. Overall, my results indicated that biodiversity and ecosystem processes responded quite differently to environmental change, but strong links existed between certain species combinations and ecosystem functions, particularly at lower trophic levels. Furthermore, the biotic and abiotic context was crucial in determining the strength of this relationship.

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