Collabrative Research: Does productivity drive diversity or vice versa? Empirical and theoretical investigations of the multivariate productivity-diversity hypothesis in streams

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The relationship between species diversity and the productivity of ecosystems is one of the most important yet controversial topics in biology. Historically, biologists have assumed that the productivity of an ecosystem limits how many species can coexist in that system. Over the past two decades, experiments have suggested that the opposite is true; that the number of species present in the same ecosystem limits the productivity. This has led to an apparent paradox: is species diversity the cause or the consequence of productivity? This study seeks to resolve this paradox by testing the Multivariate Productivity-Diversity hypothesis. This hypothesis proposes that the relationship between productivity and diversity can be distilled into three types of effects: 1) an effect of nutrient supply that sets an upper bound on an ecosystem's potential productivity, 2) an effect of species richness that determines how productive an ecosystem actually is for a given nutrient supply, and 3) an additional effect of nutrient supply on production that occurs as nutrients control the number of competing species that can coexist. This research will use field and laboratory experiments to quantify these effects and fit them together into a mathematical model that predicts both the biomass and number of species of plants and animals in an ecosystem. This research will have significant broader impacts on the management of ecosystems that are undergoing rapid environmental change. Species diversity is being lost worldwide at an unprecedented rate, and the productivity of ecosystems is being altered by over use of fertilizer. This work will be at the forefront of developing models that help forecast how two of the most pervasive aspects of environmental change (biodiversity loss and excessive nutrients) jointly impact ecological communities. This project will also provide research training to graduate and undergraduate students.