Fig. 1.

Schematic of expected host–phage interaction matrices (white cells denote infection). (A) Host–phage interactions are unique (i.e., only one phage infects a given host, and only one host is infected by a given phage). (B) Host–phage interactions are modular (i.e., blocks of phages can infect blocks of bacteria, but cross-block infections are not present). (C) Host–phage interactions are nested (i.e., the generalist phage infects the most sensitive and the most resistant bacteria, whereas the specialist phage infects the host that is infected by the most viruses). (D) Host–phage interactions are random and lack any particular structure. For B–D, a connectance of 0.33 was used so that the expected total number of interactions was the same in each case.