Variety of environments known to be inhabited by microbes. Ranges of environmental fluctuations (latitude, pH, salinity, and temperature) where microbes can be found are also shown (see Madigan and Marrs 1997; Madigan et al. 2003; Konhauser 2007). Direct and indirect interactions between different microbial communities, as well as symbiotic associations, coevolution, and horizontal genetic exchange (e.g., Davison 1999; Gogarten et al. 2007) are assumed to drive and have driven ecological processes and adaptations to habitat variability.