Elevational Gradients Impose Dispersal Limitation on .

Dispersal governs microbial biogeography, but the rates and mechanisms of dispersal remain poorly characterized for most microbial taxa. Dispersal limitation is driven by limits on dissemination and establishment, respectively. Elevation gradients create striking patterns of biogeography because they produce steep environmental gradients at small spatial scales, and these gradients offer a powerful tool to examine mechanisms of dispersal limitation. We focus on , a bacterial genus common to soil, by using a taxon-specific phylogenetic marker, the RNA polymerase-encoding gene. By targeting , we assess dispersal limitation at finer phylogenetic resolution than is possible using whole community analyses. We characterized diversity at local spatial scales (100 to 3,000 m) in two temperate forest sites located in the Adirondacks region of New York State: Woods Lake (<100 m elevation change), and Whiteface Mountain (>1,000 m elevation change). Beta diversity varied considerably at both locations, indicative of dispersal limitation acting at local spatial scales, but beta diversity was significantly higher at Whiteface Mountain. Beta diversity varied across elevation at Whiteface Mountain, being lowest at the mountain's base. We show that taxa exhibit elevational preferences, and these preferences are phylogenetically conserved. These results indicate that habitat preferences influence biogeography and suggest that barriers to establishment structure communities at higher elevations. These data illustrate that biogeography is governed by dispersal limitation resulting from a complex mixture of stochastic and deterministic processes.