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These studies did not suggest that broad taxonomic groups are more or less sensitive to disturbances than narrow taxonomic groups. This pattern suggests that taxonomic breadth is not related to whether a compositional shift was detected. Perhaps more surprisingly, there are no patterns suggesting that methodology influences whether a compositional change was detected. In addition, we were not able to discern whether particular taxonomic or functional groups are more or less sensitive to particular disturbance types. Overall, the low number of studies observing a resistant microbial composition hinders our ability to recognize any patterns among these studies. However, we can conclude that microbial composition is generally sensitive to disturbance.

RESILIENCE OF MICROBIAL COMPOSITION

Even if microbial composition is sensitive to a disturbance, the community might still be resilient and quickly return to its predisturbance composition. A number of features of microorganisms, and in particular Bacteria and Archaea, suggest that resilience could be common. First, many microorganisms have fast growth rates; thus, if their abundance is suppressed by a disturbance, they have the potential to recover quickly. Second, many microbes have a high degree of physiological flexibility. This is famously the case for the purple nonsulfur bacteria, which can be phototrophs under anoxic conditions and heterotrophs under aerobic conditions. Thus, even if the relative abundance of some taxa decreased initially, these taxa might physiologically acclimate to the new abiotic conditions over time and return to their original abundance. Finally, if physiological adaptation is not possible, then the rapid evolution (through mutations or horizontal gene exchange) could allow microbial taxa to adapt to new environmental conditions and recover from disturbance. All of these arguments assume that abundance is reduced by a disturbance, but some microbial taxa may benefit from the new conditions and increase in abundance. Thus, in order for some taxa to recover in abundance, those that responded positively to the disturbance would also need to decrease in abundance to return the community to its original composition.

Few studies explicitly focus on the time course of microbial composition after a disturbance; instead, most focus solely on the sensitivity of composition. Consequently, we recorded the length of time between the application of the disturbance and when microbial composition was assessed for the studies in our sample. If composition is highly resilient, then one should be less likely to detect a compositional change as time from disturbance increases.

We compared the time from initial disturbance for those studies that found composition to be sensitive versus resistant. Generally, the tim-



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