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 chlorophyll a and periphyton C:P and N:P. The divergent relationships of periphyton chlorophyll a and stoichiometry with invertebrate richness suggest that autochthonous resource quantity limits diversity more than quality, consistent with patterns of eutrophication. Collectively, we provide evidence that patterns in resource quantity and quality play important, yet differing roles in shaping freshwater biodiversity across spatial scale. The importance of resource quality to cross-scale patterns in biodiversity 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. We provide evidence that resource quantity and quality play important, yet differing roles in shaping freshwater biodiversity across spatial scale. Photo credit: J.J. Giersch.image

Automated summary

The relationship between resource quantity and quality and species richness at different spatial scales was evaluated in this study. It was found that at the local scale, species richness peaked at intermediate levels of resource quantity (chlorophyll a), but had a shallow negative relationship with resource quality (periphyton C:P and N:P). However, at the regional scale, species richness had a strong negative relationship with resource quantity and quality. This suggests that resource quantity has a greater impact on biodiversity than resource quality, consistent with patterns of eutrophication.