This proposal tests the species diversity-ecosystem function paradigm across fish functional groups in temperate streams. To date the PIs have shown that single fish species can affect ecosystem properties such as primary production (PPR), benthic invertebrate abundance, and organic matter processing rates in midwestern USA streams. Further, fish diversity enhances ecosystem function via functional complementarity. In the proposed research, mechanisms of fish ecosystem effects will be investigated using species from three putative functional groups including: (1) benthic invertivores that may increase PPR through a trophic cascade, (2) surface feeding insectivores that may increase PPR through nutrient enhancement of the ecosystem, and (3) benthic invertivore-disturbers that may increase PPR through trophic cascade and bioturbation. The proposed experimental design will systematically eliminate each potential mechanistic pathway between the fish and the ecosystem response, providing a definitive answer as to which mechanisms drive the responses. Overall, this research will give a more comprehensive understanding of how specific fishes and fish diversity affect stream ecosystem properties, and broaden general knowledge of the relationship between diversity and ecosystem function.
