Beta diversity of stream diatoms at two hierarchical spatial scales: implications for biomonitoring

Abstract

Summary Human‐induced loss of environmental heterogeneity may lead to homogenisation of biological communities. However, environmental heterogeneity is important for sustaining current levels of biodiversity. Hence, more ecological research should be directed on understanding the relationships between beta diversity and environmental heterogeneity. Benthic diatoms are among the most extensively studied taxa of primary producers in streams, yet their beta diversity patterns are not well documented at intermediate spatial scales, that is within and among streams, in a catchment. We tested how well one sampling site represents the total diatom diversity of a stream using 10 boreal streams, each comprising 10 sampled riffles. We also examined variation in diatom community structure at two hierarchical scales, within and among streams. Relationships between diatom beta diversity and environmental heterogeneity were studied using a combination of species accumulation curves, canonical analysis of principal coordinates, tests of homogeneity of dispersions and distance‐based redundancy analysis. We found large variation in community structure within each stream, which indicates thatone sample is not adequate to represent the diatom diversity of an entire stream. The variation in among‐stream diatom community structure was larger than among‐stream habitat heterogeneity. Although no positive relationship between within‐stream diatom beta diversity and environmental heterogeneity was detected, we found that diatom community variation was significantly related to physical habitat structure and, surprisingly, also to grazer abundance. We recommend that more than one sampling site is included in analyses aiming to cover the diatom diversity of a whole stream. This is especially true for pristine sites with high diatom diversity. In addition, we suggest that researchers incorporate physical and biological factors as explanatory variables when monitoring diatoms both at the within‐ and among‐stream scales.