With environmental conditions in a contiguous system has never been addressed. In this study we examined taxonomic and functional biogeography in the context of the selective pressures in the Great Salt Lake, Utah. GSL is a hypersaline environment where NaCl concentration ranges from near seawater to saturation, with exceptionally high concentrations of sulfate and heavy metals KRX-0401 throughout the lake. We analyzed the microbial biodiversity and functional potential across nine sites, chosen for extremes in salt concentration, throughout GSL. Because the majority of environmental microbes cannot be cultured with current laboratory techniques, we utilized recent advances in environmental microarray technology to profile the community structure and functional gene characteristics. In general, higher salt conditions are restrictive to Cyanobacteria, b-proteobacteria, and Bacteroides, and favor Archaea and Thermotoga. We suggest that the variation in functional diversity within these communities may reflect the environmental dynamics associated with each location. Because of its direct link with the functional repertoire, the diversity of function in relation to the diversity of organisms is believed to be closely coupled to the functional complexity and environmental niche of an organism. Unvarying environmental conditions favor organisms with a narrow functional repertoire of genes while variable environmental conditions favor versatile organisms with a wide range of functional potential. Ratios of gene richness to phylogenetic richness in two longterm sites when compared with USGS abiotic measurements suggest that more versatile organisms are found in areas that vary greatly in oxygen concentration. Although variations in oxygen are not responsible for driving all genetic diversity, these data suggest that environmental pressures drive functional diversity in GSL and are consistent with metagenome analyses of HGT. Consequently, the distribution and frequency of functional genes throughout different communities provide insight to environmental pressures experienced by these microbial consortia. The functional gene array provides a powerful tool for studying microbial biogeography and ecosystem dynamics in various environments. The functional gene array has sufficient resolution at the functional level to demonstrate how changes in environmental conditions affect the functional structure of microbial communities. In addition, it offers some predictive value with respect to estimating enzymatic activities in microbial communities related to gene families, making correlations between gene abundances and ecological significance rather straightforward. Moreover, the number of gene variants detected offers insight to possible functional redundancy among the dominant community members, while absolute hybridization intensity is indicative of relative abundance of genes. Resource limitation often drives selection through competitive exclusion where groups more adept at acquisition and more efficient at resource utilization excel, resulting in fewer competitors.