Bacterial Diversity in Freshwater

The tree of life, describing the evolutionary relationships among organisms, is totally dominated by bacteria. In a regular ecology textbook, the number of bacterial and Archaeal examples are, however, few. Microorganisms are in many respects understudied, and we do not yet know if they follow similar “rules” as other organisms: for instance, regarding patterns in diversity over time and space. Further, bacteria play important roles in biogeochemical cycles, and therefore it is also important to understand if and how this enormous diversity is related to the role bacteria play in ecosystems. Despite methodological developments (see Historical Overview and Methods) that led to an exponential increase in the amount of data over time, we are still only scratching the surface of the diversity of freshwater bacteria (see Measuring Alpha Diversity), and few general patterns in diversity have emerged. Some typical freshwater bacterial groups have been identified (see Marine and Freshwater Bacterioplankton and Typical Freshwater Bacteria) and some important environmental steering factors are known (see Biogeography of Freshwater Bacteria). Further, a consistent pattern appears to be that alpha diversity decreases along lake and river chains because of inoculation of bacteria from species-rich soils (see Patterns in Alpha Diversity). Some findings of bacterial alpha diversity further indicate that bacterial diversity may not always follow the same rules as in larger organisms, challenging some established textbook “truths” regarding what is influencing diversity in general. But more data is needed for certain conclusions. Future work should also include the identification of the true (active) players and their possible importance for ecosystem functioning (see Identifying Contributors to Community Functioning).