Upper panels: distribution of the SFRD at different metallicities and redshifts (z). Left: background colour and brown contours show the high metallicity extreme assuming the non-universal IMF, and white contours show the high metallicity extreme assuming a universal IMF. Right: same as in the left panel, but for the low metallicity extreme. To plot the white contours, f_SFR(Z, z) for the universal IMF cases has been re-scaled in such a way that the total SFRD at each redshift matches that of the corresponding variation with the non-universal IMF (see the bottom panel; the non-scaled f_SFR(Z, z) in the universal IMF cases is shown in Fig. 8 in ChN19). This reveals the presence of the more extended low-metallicity tail present in the non-universal IMF variations. Bottom panel: ratio of the total SFRD at each redshift as calculated under the assumption of the non-universal to universal IMF for the two f_SFR(Z, z) variations (dashed line – low-Z extreme, solid line – high-Z extreme).