The aim of the study was to examine the strength of abundance and occupancy of bacterial communities inhabiting Saint Lawrence estuary along taxonomic ranks.

Abundance-occupancy relationships (AO) is a relation describing the abundance and the number of sites that each speices attain on a regional scale. Quantifying the strength of AO relationships in microbial communities in natural systems incorporated with phylogenetic framework and life-history styles is currently not known. Here we assessed the strength of AO relationships along taxonomic ranks within particle-attached (PA) and free-living (FL) assemblages across depth in Sanit Lawrence Estuary, and estimated the slope of the relataionships serving as niche divergence rates. We found the strongest strength of the associations at the class level, and such patterns were consistent within the two lifestyles. The niche divergence rates were significantly higher at the phylum than the other levels, the degree of which may depend on the lifestyles of bacteria. Overall, the study suggests that broad taxonomic resolution sufficiently delineates the relationships between niche breadth and phylogenetic relatedness among bacterial taxa with differing lifestyles.