Ecological uniqueness of stream and lake diatom communities shows different macroecological patterns.

Aim To discover whether lake and stream diatom communities show different patterns in species richness and in their local ( LCBD) and species ( SCBD) contributions to beta diversity in relation to macroscale environmental characteristics. Location Finland. Methods As biological data, we used diatom samples collected from Finnish stream ( n = 492) and lake ( n = 290) sites. As explanatory variable data, we used information on macroscale environmental and historical aspects, such as bedrock, soil and post-glacial highest shoreline. We also accounted for catchment areas, different levels of isolation and relative centrality of the study sites. We ran multiple linear models and selected best models based on AICc values. Results We found that macroscale factors affecting diatom richness and ecological uniqueness differed clearly between streams and lakes. LCBD and species richness of stream communities were more affected by regional environmental characteristics, whereas LCBD and species richness of lake communities were more often driven by spatial measures. The measures of LCBD and species richness showed a slightly negative relationship in streams, but no such relationship was detected in lakes. Also, we showed that, for both streams and lakes, SCBD was strongly determined by the number of sites occupied by a species and the overall abundance of a species. Main conclusions Our findings related to the distinction between the determinants of lake and stream species richness or LCBD may be tied to the different hydrological connectivity levels occurring in freshwater lotic and lentic systems. Also, in streams, sites with exceptional ecological uniqueness seem to have a rather low number of species. Our findings may be applied to biological conservation and monitoring planning, emphasizing that not only species-rich but also unique low-richness sites may be valuable conservation goals. [ABSTRACT FROM AUTHOR]