Biodiversity: Illustrations of some concepts, causes, and consequences (New Zealand, Oregon)

Careful analysis and thoughtful synthesis will be necessary for expanding the envelope of ecological understanding. This work is my attempt at communicating both of these, in relation to three questions about our understanding of the structure and dynamics of biological diversity. These questions focus on (a) advancing our understanding of the relations of organismal form and physiological process, (b) explaining the overwhelming influence of ecological context on the relationship between local ecological processes and regional evolution and dispersal processes in driving local species richness patterns, and (c) demonstrating the causal effect of biological trait diversity on community photosynthetic processes. Chapter two addresses how we conceptualise diversity, and concludes that although simple (i.e., univariate) morphologically-based functional group models for macroalgae are not functionally predictive, morphology does play a key role in ecophysiological responses. Using morphological attributes to successfully infer macroalgal behaviour would be a remarkable advance for marine ecology, and appears attainable. Chapter three demonstrates the overwhelming importance of ecological context in altering the predictions of theory. Specifically, we demonstrate that regional species pools have reduced influence on local richness at small local scales, within interactive groups of species, and in higher intertidal zones. We conclude with a synthesis of how ecological competition, abiotic stress, and positive interactions may act in concert to influence local richness. Chapter four analytically investigates the role of diversity in changing how ecosystems function. I argue that all effects of diversity must act through species traits, and that the current debate regarding the influence of species richness per se versus species traits is misguided. Instead, I propose a focus on the roles of the presence of, versus interactions between, traits. I provide empirical evidence that five tidepool communities each containing five species have a higher average photosynthetic rate than the same total biomass of each of the five species arranged into five monocultures. This mechanism, detected in photosynthetic rate (one of the most fundamental ecological functions), should be common to ecosystems other than marine intertidal pools. Finally, chapter five concludes with a recap of the key results from these studies, and a look to the future.