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Notes on “Power law rank-abundance models for marine phage communities” by Hoffman et al. (2007)

“Contrary to other power law scenarios, which show a type of stability where the rich stay rich, in this model the dominant phage keeps changing.”

“The model of this study makes four assumptions that lead to the rank– abundance relation. [...] The first assumption is that different predator–host pairs do not interact. [...] It is further assumed that there is a strong and specific interaction between a microbial host and its phage predators, which results in the most abundant microorganism (bacteria and archaea) being killed by its phage predators. This relationship has been termed ‘kill the winner’ and it predicts that specific predator–prey pairs oscillate in time as blooms of a particular microorganism are followed closely by blooms of its phage predator (Thingstad, 2000). The third assumption is that all phage–host pairs follow identical dynamics, but bloom at independent times (i.e. they are randomly distributed in time along a common cycle). This hypothesis bears some resemblance to the hypothesis of neutral evolution; it is expected that the qualitative features are captured by replacing the full complexity of the problem by one ‘average’ type.”

In their model, the population of phages cycle from being low (and thus rare) to large (and thus abundant). This is not an explanation of the power-law relationships described by Suttle (2005). It does not explain why the abundant viruses are the ones that have a fast growth rate (in part due to their simplified metabolism, i.e. sample genome) and attack microbes that have also a fast growth rate yet are the rarest of the microbes. The authors say that they try to model what Thingstad (2000) describes. I need to read that paper.

“The buildup of the microorganisms is relatively slow and approximately exponential. The subsequent buildup of phage and dropoff of the microorganism population are very rapid. In general, the phage bloom is much shorter than the microorganism bloom.”

“The better fit of the GLV over LV might be interpreted biologically as representing the cooperative nature of phage predation in a local spatial–temporal region.”