Local–global overlap in diversity informs mechanisms of bacterial biogeography

Joshua A Livermore and Stuart E Jones

Spatial variation in environmental conditions and barriers to organism movement are thought to be
important factors for generating endemic species, thus enhancing global diversity. Recent microbial
ecology research suggested that the entire diversity of bacteria in the global oceans could be
recovered at a single site, thus inferring a lack of bacterial endemism. We argue this is not the case in
the global ocean, but might be in other bacterial ecosystems with higher dispersal rates and lower
global diversity, like the human gut. We quantified the degree to which local and global bacterial
diversity overlap in a diverse set of ecosystems. Upon comparison of observed local–global diversity
overlap with predictions from a neutral biogeography model, human-associated microbiomes (gut,
skin, mouth) behaved much closer to neutral expectations whereas soil, lake and marine
communities deviated strongly from the neutral expectations. This is likely a result of differences
in dispersal rate among ‘patches’, global diversity of these systems, and local densities of bacterial
cells. It appears that overlap of local and global bacterial diversity is surprisingly large (but likely not
one-hundred percent), and most importantly this overlap appears to be predictable based upon
traditional biogeographic parameters like community size, global diversity, inter-patch environmental
heterogeneity and patch connectivity.