<p><b>A</b>. NMDS ordination of 16S rRNA gene-derived microbial community structure. Similarity profile analysis, an <i>a priori</i> statistical approach that uses permutation to identify groups of communities that are more dissimilar than expected by chance, identified two distinct clusters of communities. Ellipses represent the 95% confidence intervals around the centroid for each cluster (the spatial mean in NMDS space of the communities belonging to each cluster). Lines emanating from the centroids indicate to which cluster each community belongs. Bacterial families well-correlated with the ordination (r<sup>2</sup> > 0.40) are displayed; vector length is proportional to the Pearson correlation coefficient for each family and vector direction corresponds to the direction of increasing abundance relative to the ordinated communities. Legend indicates the dune from which each ordinated community originated. Final 2-dimensional stress of the ordination is 0.12. <b>B</b>. Linear discriminant analysis (LDA) of bacterial classes indicates that the two clusters of microbial communities identified by similarity profile analysis are driven by the disparity between a high abundance of <i>Gammaproteobacteria</i> in one set of communities and more diverse population in the other set of communities. Only classes with effect size > 2.0 are displayed. <b>C</b>. NMDS ordination is based only on samples for which environmental parameters were measured. Parameters with r<sup>2</sup> > 0.1 are displayed. Final 2-dimensional stress of the ordination is 0.07.</p
