Fig. 1: Community ecological model of viral and grazer mediated predation; and SCOPE HOE-Legacy 2A cruise field data.

a Prochlorococcus are structured by infection status. Viruses (V) can infect susceptible Prochlorococcus cells (S) generating infected cells (I). Viral-induced lysis of infected cells releases virus particles back into the environment. Susceptible and infected Prochlorococcus cells are subject to grazing pressure from heterotrophic nanoflagellate grazers (G). Grazers may have a generalist strategy (e.g., grazing on heterotrophs, mixotrophs, and phytoplankton not represented by S and I). We specify six models along this specialism-generalism gradient by setting a parameter γ. When γ = 0 heterotrophic nanoflagellate grazers act as specialists and only consume Prochlorococcus; and as γ increases, Prochlorococcus constitutes less of the diet of heterotrophic nanoflagellate grazers. Parameters and units are specified in Table S2. b Reported empirical population dynamics of Prochlorococcus cells⁷⁴, the percentage of Prochlorococcus cells infected with T4/T7-like cyanophage²², the abundance of free-living T4/T7-like cyanophage²², and the abundance of heterotrophic nanoflagellate grazers²³. c Cruise track and sampling stations. Local times (HST) for the start and end of recorded underway sampling (black line), and first and last sampling stations (red points) are annotated.