COS 11-9
A macroecological investigation of the microbial “rare biosphere”
The microbial “rare biosphere” refers to the common observation that microbial communities are mainly composed of rare taxa. Though communities of conspicuous plants and animals are characterized by a similar pattern, degrees of rarity are assumed to be exceptional among microbes. While the rare biosphere is potentially explainable in terms of the biology of microbes and sampling methods, the question remains as to whether observed patterns of commonness and rarity actually differ between microbes and macrobes and, if so, whether these differences can be attributed to unique properties of microbial life. To address this question, we compared aspects of abundance, dominance, evenness, and rarity across a large compilation of aquatic, terrestrial, and host-related microbial community data to similar aspects across a large compilation of count data from sites of bird, mammal, insect, and tree communities.
Results/Conclusions
Microbial communities were characterized by higher degrees of rarity and lower evenness than those of macrobes. Much of this appears to be due to greater values of total abundance in microbial communities. Likewise, microbial community datasets often include many phyla while macrobial datasets rarely include more than one class. We parsed microbial datasets into taxonomic levels that were more comparable with macrobes. At this level, degrees of rarity and evenness between microbes and macrobes were indistinguishable. Despite manifold differences in how taxa are delimited and how abundance is estimated, the microbial rare biosphere is consistent with general patterns expected at large scales of abundance and taxonomic richness. While detailed aspects of the rare biosphere deserve greater attention, microbial communities may reveal how the forms of general ecological patterns should appear at the upper limits of abundance and diversity.