Macroevolutionary constraints on global microbial diversity

Abstract

Biologists have long sought to quantify the number of species on Earth. Often missing from these efforts is the contribution of microorganisms. Despite recent large-scale sampling efforts, estimates of global microbial diversity span many orders of magnitude. To reconcile this uncertainty, it is important to consider how speciation and extinction over the last four billion years constrain inventories of biodiversity. We parameterized macroevolutionary and mass-extinction event models to determine how diversification limits present-day microbial diversity. We find that while 106-107 taxa is most probable, much larger values ([≥]1012) are feasible. Allowing for mass extinction events does not greatly alter these conclusions. Along with empirical predictions, our models provide support for a massive global-scale microbiome while shedding light on the upper limits of life on Earth.