Resource quantity and quality differentially control stream invertebrate biodiversity across spatial scales

Resource quantity controls biodiversity across spatial scales, however the importance of resource quality to cross-scale patterns in species richness has seldom been explored. We evaluated the relationship between stream basal resource quantity (periphyton chlorophyll-a) and invertebrate richness and compared this to the relationship of resource quality (periphyton stoichiometry) and richness at local and regional scales across 27 North American streams. At the local scale, invertebrate richness peaked at intermediate levels of chlorophyll-a, but had a shallow negative relationship with periphyton C:P and N:P. However, at the regional scale richness had a strong negative relationship with both chlorophyll-a and periphyton C:P and N:P. The divergent effects of periphyton chl-a and stoichiometry on invertebrate richness suggest that basal resource quantity limits diversity more than resource quality, consistent with patterns of eutrophication. Collectively, we demonstrate that resource quantity and quality play important, yet differing roles in shaping freshwater biodiversity across spatial scale.

Methods
This database was generated by downloading and compiling publically available data from the National Ecological Observator Network (NEON). NEON encompasses 27 stream and river sites across the continental U.S. from Alaska to Puerto Rico. The NEON sites span a variety of biomes including montane, subtropical and temperate forests, tundra, and desert. Between 2017-2021, sampling of ecological variables was repeated one-four times per year depending on measurements and site accessibility. In this dataset, we included: periphyton chlorophyll-a (hereafter chl-a), periphyton stoichiometry (Molar C:N:P), benthic invertebrate community composition, total water column nitrogen, and phosphorus, fish density, and stream discharge. For a more detailed description of NEON sampling procedures for all response variables used in this study see (https://data.neonscience.org/home).