Microbial macroecology:: highly structured prokaryotic soil assemblages in a tropical deciduous forest

Aim To assess the hypothesis that free-living prokaryotes show a pattern of 'no biogeography' by examining the scaling of soil prokaryotic diversity and by comparing it with other groups' biogeographical patterns. Location Two sites in the tropical deciduous forest of Chamela, Jalisco, on the western coast of Mexico. Methods We examined the diversity and distribution of soil prokaryotes in two 8 x 8 m quadrats divided in such manner that we could sample at four spatial scales. Restriction fragment length polymorphisms of 16S rRNA genes were used to define operational taxonomic units (OTUs) that we used in lieu of species to assess diversity. Results We found highly structured species assemblages that allowed us to reject multiple predictions of the hypothesis that soil bacteria show 'no biogeography'. The frequency distribution of range size (measured as the occupancy of quadrats) of OTUs followed a hollow curve similar to that of vertebrates on continents. Assemblages showed high levels of beta diversity and a non-random nested pattern of diversity. OTU diversity scaled with area followed a power function with slopes z = 0.42 and 0.47. Main conclusions We demonstrate a non-ubiquitous dispersal for soil prokaryotes, which suggests a complex biogeography similar to that found for terrestrial vertebrates.