Ubiquitous microbes and ecosystem function

Until recently, microbial diversity was the least well understood component of biodiversity. But free-living microbes have some unique characteristics, and it is now believed that these may simplify the task of understanding biodiversity at the microbial level. Microbes have astronomical abundance on a global scale. As a consequence, species are ubiquitous, so speciation and extinction are rare, the global number of microbial species is relatively small, and local species richness is a large proportion of global species richness. At some critical point on the continuum of increasing organism size, loca1:global species richness ratios will begin to decrease and the proportion of the world's taxa represented at a single site will begin to fall. The organism size range marking this 'ubiquity-biogeography' (U-B) transition is unknown but is unlikely to extend below I mm. As "everything (microbial) is everywhere", ecosystem functions will rarely, if ever, be limited by lack of microbial diversity.