The biogeography of stream bacteria

Aim The extent to which bacterial communities exhibit biogeographic patterns in their distribution remains unclear. We examined the relative influence of factors including geographic distance, latitude, elevation and catchment land use on the distribution and taxon richness of stream bacterial communities across New Zealand. Location Bacterial communities were collected from biofilm growing on submerged rocks in 244 streams. Sample sites spanned a northsouth gradient of over 970km, an elevational gradient of c. 750m and were collected from a variety of catchment types across New Zealand. Methods We used automated ribosomal intergenic spacer analysis, a DNA fingerprinting technique, to characterize the structure and taxon richness of each bacterial community. Key attributes relating to sample location, upstream catchment land use and a suite of additional environmental parameters were collected for every site using GIS procedures. Univariate correlations between measures of bacterial community structure and latitude, elevation and distance were examined. Variance partitioning was then used to assess the relative importance of purely spatial factors versus catchment land use and environmental attributes for determining bacterial community structure and taxon richness. Results Bacterial taxon richness was related to the geographic location of the sample site, being significantly greater at latitudes closer to the equator and reduced at higher elevations. We observed distance decay patterns in bacterial community similarity related to geographic distance and latitudinal distance, but not to elevational distance. Overall, however, bacterial community similarity and taxon richness was more closely related to variability in catchment land use than to climatic variability or geographic location. Main conclusion Our data suggest that stream biofilm communities across New Zealand are more influenced by catchment land use attributes than by dispersal limitation.