for such changes to influence model predictions. This assumption may be valid if microbial composition is resistant, resilient, and/or functionally redundant (these terms and others are defined in Table 8.1). Microbial composition is resistant if it is similar across a variety of environmental conditions—in other words, it is difficult to perturb from an original state. It is resilient if, when composition does change, it recovers quickly, whether by growth or by physiological or genetic adaptation. Finally, microbial composition may change in response to new environmental conditions but contain functionally redundant taxa such that ecosystem process rates are not altered. If these conditions are not generally true for microbial communities, then many current ecosystem models may fail at predicting the rates of microbe-driven processes under disturbance.

The idea that microorganisms are resistant, resilient, and functionally redundant is pervasive in ecology. Some microbial groups show a high degree of metabolic flexibility and physiological tolerance to changing environmental conditions [e.g., Meyer et al. (2004)], which could result in microbial communities that are resistant to change. These traits and others associated with microbes—such as high abundances, widespread dispersal, and the potential for rapid growth rates—have also led to the suggestion that microbial communities will be resilient to change (Fenchel and