Rule number one of cooperative bacterial warfare? Be in the majority.

Current Biology “Positively Frequency-Dependent Interference Competition Maintains Diversity and Pervades a Natural Population of Cooperative Microbes”

This is another great example of how theory that does not consider space is a poor representation of nature. Here, the diversity of a soil bacterium (Myxococcus xanthus) is shown to be potentially explained by positive frequency-dependent selection, the phenomenon by which those individuals in the majority maintain advantages over those in the minority. If you consider a well-mixed population, positive frequency-dependent selection ought to purge diversity, as individuals at low frequency are at a competitive disadvantage. But a so-called “well-mixed” population is also really unrealistic in many real situations, as the frequency of a particular trait is considered globally rather than locally. If you are a soil bacteria, it is the frequency of local competitors and comrades that matters, not the global frequency. This study demonstrates that when these local effects dominate, positive frequency dependence can produce — rather than reduce — diversity.