Functional diversity and environmental context shape community processes in an experimental aquatic ecosystem

The relationship between biodiversity and ecosystem function has emerged as a vital concept in conservation biology. Elevated biodiversity has been shown to influence critical ecosystem processes; however, the identity of species composing a community may be more important than the absolute number of species. Previous research has focused on how producer diversity affects ecosystem functioning without considering environmental context. Here we assess the effects of consumer species richness on aquatic ecosystem processes under different habitat contexts in a mesocosm experiment. Species richness and habitat substrate were manipulated using a 3x2 factorial design. Substrate was either sand or gravel, and 3 species (amphipods, water boatmen, and snails) were maintained at 0, 1 and 3 species across 54 plastic tubs. Species densities were established across species treatments such that total species biomass was held constant. After 21 days, increasing richness from one to three species significantly decreased periphytic biomass by 22%, periphytic chlorophyll by 25%, and suspended chlorophyll by 19% (ANOVA, P < 0.05). Enhancing richness also resulted in increased leaf breakdown (Multiple Regression, P < 0.05). No single species effect equaled or exceeded the 3-species treatment, suggesting facilitation and complimentarity between species. Substrate type caused differences in fine particulate organic matter (FPOM) and turbidity (Multiple Regression, P < 0.05); however, no significant interactions between substrate and species richness were detected. This experiment suggests that increasing species, and more importantly, functional diversity may be important for understanding algal dynamics, primary production, and decomposition rates in aquatic ecosystems.