Using traits to explain interspecific variation in diatom occupancy and abundance across lakes and streams

Abstract

AIM: To discover how biological traits, ecological preferences and taxonomic relatedness are associated with occupancy and abundance of diatom species across lakes and streams. LOCATION: Finland. TAXON: Diatoms. METHODS: We studied 288 diatom species from 492 stream sites and 230 diatom species from 290 lake sites. For each species, we calculated logit‐transformed regional occupancy and log‐transformed mean local abundance, and further determined biological traits, ecological preferences and taxonomic levels for each species. Boosted regression tree (BRT) analysis was used to reveal the linear and nonlinear associations of biological, ecological and taxonomic predictors with occupancy or abundance of lake and stream diatoms. RESULTS: There were strong and positive interspecific occupancy–abundance relationships across both lakes and streams. The BRT models explained more deviances in variation in occupancy and abundance and their relationship for lakes than streams. Biological traits, especially cell size, but also life‐form and guild, were the strongest predictors of diatom occupancy and abundance in lakes and streams when controlling for ecological preferences and taxonomic relatedness. MAIN CONCLUSIONS: In general, biological traits were the strongest predictors of occupancy and abundance in both freshwater systems. Species with similar biological traits thus tended to show similar occupancies and abundances. As indicated by lower explained deviances, occupancy and abundance in streams seemed to be more complexly structured than in lakes, suggesting that these two freshwater system types differ in the formation of biodiversity patterns. This difference may be related to the differences in hydrological connectedness between lakes and streams. Understanding how variations in species’ occupancy and abundance are formed across various waterbodies is important for meaningful biodiversity conservation.