Species area relationship (SAR) for benthic diatoms: a study on aquatic islands

The question of how species richness depends on the area is one of the most intensively studied subjects in biogeography. Many studies have reported this pattern for terrestrial and macroscopic taxa; however, microscopic and aquatic communities have received much less attention in the literature. The aim of our study was to reveal the relationship between the habitat size and richness of freshwater benthic diatom assemblages. We hypothesized that if the size of studied water bodies covers wide spatial scales, the species-area relationship (SAR) could be described by a sigmoid model. Benthic diatom assemblages were investigated in pools, ponds and lakes of various sizes (10(-2)-10(8) m(2)). We demonstrated that although the SAR in the log-log space can be described by a linear model, the linear breakpoint regression provides better fit to data. Using this technique a characteristic small island effect (SIE) could be distinguished. The SIE fell in the range of 10(-2)-10(4) m(2). We also demonstrated that species richness of the diatom guilds is remarkably different in the various size ranges of the water bodies. We also demonstrated that the slope of the SAR (z value) is similar to those values that have been reported for other microbial organisms.