The principle of competitive exclusion is apt here as the conditions of a single limiting resource and as assumption of spatially independent communities. As selective pressure increases, the functional redundancy throughout the community declines with an increase in abundance of functionally similar and competitive variants. For example, high concentrations of chromium throughout GSL provide a selective advantage for organisms containing the most effective chromium resistance strategies. These more efficient mechanisms increase within the population and ineffective resistance mechanisms disappear due to toxicity of the environment. The ratio of the relative intensity to relative richness, therefore, provides a metric for the selective pressure throughout GSL. Conversely, the absence of selective pressure allows diversification of genes as less efficient variants pose no threat to fitness. Sulfate concentration in the GSL is extremely high and is not likely a limiting factor in microbial growth. Consequently, there is little selective pressure for more efficient sulfate reduction genes resulting in more variants and no dominant variants. In this case, the relative intensity is low whereas the number of gene variants is high. Variation in function, presumably via HGT, rather than changing community, is controlling gene distribution within the environment. Beta-diversity describes the change in biodiversity over space, time, or environmental gradients and often provides ecological and evolutionary information on dispersal, speciation processes, and species turnover. Generally, beta-diversity is used to quantify the species change or turnover in order to delineate biotic regions or transitions. In the case of this study, we use betadiversity to quantify the spatial change of functional genes within the environment. Biodiversity studies are often hampered by artifacts BIBW2992 associated with sampling which in this case is minimized using array technology. Each array contains probes for about ten thousand genes, and hence a single hybridization can simultaneously survey a good portion of microbial populations. Despite being a closed format that provides information only about the genes present on the microarray, the Phylochip and GeoChip ensure unbiased comparison of microbial communities because each community is tested against the same set of probes. Although the scale makes a difference in conclusions based on biodiversity estimates, both arrays used here are based on the gene-level scale. In order to treat the two different approaches cautiously, we looked at the presence/absence for genes and community members. The average similarity decay of 16S rRNA genes is low throughout GSL, translating into dispersal limitations presumably due to the salinity gradient. The similarity of all functional genes is significantly higher than that of 16S genes, indicating higher dispersal for all functional gene groups analyzed. These observations are comparable with studies that show a difference in the historical rate of gene transfer between informational genes.