River benthic diatom assemblages exhibit biogeographical patterns even at small scales

Abstract Understanding the geographical and environmental drivers of α- and β-diversity is essential in biogeography and ecology. Biogeographical patterns of microorganisms are harder to define and interpret compared to larger organisms, and are mostly apparent on broad regional scales. This study examines biodiversity patterns of benthic diatoms at a smaller scale, i.e. in Greek rivers. We used 233 sites across four biogeographical areas defined by freshwater fish communities. We investigated Species-Area Relationships and α-diversity patterns through taxonomic and functional richness and β-diversity using the Sorensen index on presence-absence data in each biogeographical area. Our findings revealed a positive relationship between species richness and drainage area of river basins. Moreover, α-diversity was higher in northern Greece, whereas β-diversity differentiated communities of western Greece through species turnover, highlighting spatial influences. Environmental variables correlated with taxonomic α-diversity but not with taxonomic or functional β-diversity. This study constitutes the first effort to investigate different biodiversity components of benthic diatoms in a Balkan hotspot by elucidating the role of spatial and environmental factors in shaping biogeographical patterns at a smaller scale. Since the emergence of biogeographical patterns is often scale and data dependent, additional data could further improve our understanding of benthic diatom diversity patterns.