There is considerable debate on whether dispersal limitation affects microbial diversity. While some studies find predominant control of local factors as drivers of microbial community composition, others point at the existence of regional species pools by finding spatial autocorrelation with regard to species richness. Using a large observational dataset on lake phytoplankton, we study how lake productivity affects community turnover at the local and at the regional level.
Results/Conclusions

We show that local (=temporal) community turnover increases with lake productivity. Moreover, this positive relationship translates into a positive correlation between regional-level productivity and dissimilarity among lakes. Community composition is rather predictable in oligotrophic lakes, while communities in eutrophic lakes are less predictable and characterized by high temporal turnover. Alpha- and beta-diveristy of lake phytoplankton exhibits a scale-dependent relationship with lake productivity (unimodal at the local scale, monotonously increasing at the regional scale). In spite of the short turnover times in phytoplankton, these patterns  conform surprisingly well with patterns reported for higher organisms before.