The influence of catchment variables on lake organisms is understudied. The terrestrial zone in the vicinity of lakes is, however, probably highly important for biota due to the effects on water chemistry and to various processes operating across ecosystem boundaries. We examined the relative importance of lake and catchment variables, as well as large-scale geographical factors, on the taxa richness of phyto- and zooplankton in 100 small lakes in Finland. In variation partitioning, the variability of phytoplankton richness was most strongly related to the effects of lake variables, the joint effects of lake and catchment variables, and the joint effects of all three groups of variables. Zooplankton richness, in turn, was most strongly related to the effects of lake and catchment variables and the joint effect of lake and catchment variables. The exact results of the variation partitioning depended on the catchment sizes considered in the regression models. Among lake variables, planktonic richness was strongly related to variables indicating productivity. Among catchment variables, the normalized difference vegetation index (NDVI), indicating catchment productivity, showed a relatively strong association with planktonic richness. These results provide evidence that catchment variables such as the NDVI may be efficient predictors of planktonic richness in small lakes. It is possible that individual lakes embedded in a highly productive landscape have higher taxa richness than solitary, potentially productive lakes because of the high influx of dispersing propagules from the regional pool. We also suggest that catchment variables may respond to environmental changes at different scales than the lake variables, and explicit consideration of catchment productivity would therefore be useful when planning research and monitoring programs for freshwater organisms.

Although phylogenetic approaches are useful for providing insights into the processes underlying biodiversity patterns, the studies of microbial phylogenetic relatedness are rare, especially for elevational gradients. Using high-throughput pyrosequencing, we examined the biodiversity patterns for biofilm bacterial communities that were scraped from stream stones along an elevational gradient from 1820 to 4050 m in China. The patterns of bacterial species richness and phylogenetic diversity were hollow towards higher elevations. The bacterial communities consisted of closer relatives than expected and displayed increasing terminal phylogenetic clustering towards mountain top. The increasing phylogenetic clustering with elevation contrasts reports for macroorganisms that revealed phylogenetic overdispersion at low or intermediate elevations. Because water temperature showed the strongest correlation with phylogenetic relatedness (r² = 0.516), the elevational pattern in the bacterial phylogenetic structure indicated that environmental filtering possibly due to lower temperature or more frequent temperature fluctuations increased towards higher elevations. Evidence supporting the environmental filtering on bacteria was also reflected by the orderly succession in the relative abundance of different bacterial phyla along the elevational gradient and in the high evenness of bacterial taxa at higher elevations. Overall, our results indicated that ecological processes possibly related to temperature may play a dominant role in structuring bacterial biodiversity along the elevational gradient.