Drivers of bacterial beta-diversity depend on spatial scale

Abstract

The factors driving β-diversity (variation in community composition) yield insights into the maintenance of biodiversity on the planet. Here we tested whether the mechanisms that underlie bacterial β-diversity vary over centimeters to continental spatial scales by comparing the composition of ammonia-oxidizing bacteria communities in salt marsh sediments. As observed in studies of macroorganisms, the drivers of salt marsh bacterial β-diversity depend on spatial scale. In contrast to macroorganism studies, however, we found no evidence of evolutionary diversification of ammonia-oxidizing bacteria taxa at the continental scale, despite an overall relationship between geographic distance and community similarity. Our data are consistent with the idea that dispersal limitation at local scales can contribute to β-diversity, even though the 16S rRNA genes of the relatively common taxa are globally distributed. These results highlight the importance of considering multiple spatial scales for understanding microbial biogeography.

Fig. 1.

The 13 marshes sampled (see Table S1 for details). Marshes compared with one another within regions are circled. (Inset) The arrangement of sampling points within marshes. Six points were sampled along a 100-m transect, and a seventh point was sampled ∼1 km away. Two marshes in the Northeast United States (outlined stars) were sampled more intensively, along four 100-m transects in a grid pattern.

Fig. 2.

Distance-decay curves for the Nitrosomadales communities. The dashed, blue line denotes the least-squares linear regression across all spatial scales. The solid lines denote separate regressions within each of the three spatial scales: within marshes, regional (across marshes within regions circled in Fig. 1), and continental (across regions). The slopes of all lines (except the solid light blue line) are significantly less than zero. The slopes of the solid red lines are significantly different from the slope of the all scale (blue dashed) line.