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Biodiversity and ecosystem functioning in plant-grazer systems: experimental tests in a marine benthic community.
Boyer, Katharyn*,1, Bruno, John1, Duffy, J. Emmett2, 1 University of North Carolina at Chapel Hill, Chapel Hill, NC, USA2 College of William and Mary, Gloucester Point, VA, USA
ABSTRACT- Despite intense interest in the relationship between species diversity and ecosystem functioning, the majority of research has focused at the base of terrestrial food webs, and to a lesser degree, on aquatic microbial microcosms. Whether and how biodiversity might be related to ecosystem functional processes at higher trophic levels and in other ecosystem types have received little attention. We conducted a series of experiments to explore the relative effects of marine macroalgal and grazer identity and diversity on net primary production in North Carolina hard substratum communities. As in many previous grassland studies, we found a diverse assemblage of algae to be more productive than the average monoculture, but not more productive than all component species. However, overyielding was due not only to the inclusion of some highly productive species but also to greater performance of some species in mixture than in monoculture. High algal diversity reduced consumption by a diverse assemblage of herbivores relative to consumption of the most palatable monocultures, perhaps reflecting associational benefits of proximity to chemically defended species. In manipulations of herbivore diversity, net algal biomass production was two times lower in the presence of a mixed grazer assemblage than in any of the grazer monocultures, suggesting dietary complementarity among herbivores. In a factorial manipulation of algal and grazer diversity, we calculated variance components and found the magnitude of effects to be greatest for the herbivore diversity factor. Although producer diversity enhanced net primary production, diversity at higher trophic levels may have an equivalent or greater influence on the structure and function of this, and perhaps other, ecosystems.
Key words: herbivory, diversity, productivity, algae