IS DIATOM DIVERSITY DRIVEN BY PRODUCTIVITY IN BOREAL STREAMS?

The effect of productivity on the diversity patterns has attracted ecologists especially during the last decades. Recent reviews have suggested that the productivity-diversity relationship (PDR) is typically either positive linear or unimodal. The emerged form of the PDR is often affected by the spatial scale and it has been suggested that the relationship is ranging from unimodal at local scales to positive linear at regional scales because of regional complementarity. The aim of this study was to examine the PDR at two spatial scales for stream diatoms. The relationships between total P Supply and species richness ranged from a significant negative relationship to a non-significant positive relationship within the studied regions. Across the regions, the relationship between mean total P of the region and regional species richness was unimodal, albeit non-significant. The data showed that the PDR exhibited large variability among the regions and across different spatial scales for stream diatoms. This indicated that diatom diversity was largely driven by other factors than nutrient supply in these streams. The present results also highlight the importance of gradient length in productivity for PDR and lend at least partial support to the pattern accumulation hypothesis because at high nutrient Supply, diversity tended to decrease.