The impacts of nutrient supply and imbalance on subcontinental co-occurrence networks and metacommunity composition of stream algae

The amounts and ratios of nutrients (nitrogen and phosphorus) are important determinants of producer community biodiversity and composition and their responses to climate and dispersal. However, the nutrient effects on co-occurrence network topology, particularly in freshwaters, are understudied. Here, we investigate 1) whether nutrient supply and ratio constrain topological properties of algal co-occurrence networks in streams and 2) to what extent climate and space (a surrogate for dispersal) affect co-occurrence network topology vs. metacommunity composition across nutrient supply and ratio contexts. We used a subcontinental dataset of benthic algae from 840 stream localities in the conterminous US. We constructed co-occurrence networks representing nutrient supply contexts (oligotrophic vs. eutrophic) and nutrient ratio contexts (N-limited vs. P-limited) and statistically assessed topological variability within each pair via randomization. We then used a null model framework and dir...