Ratio of the fraction of stars forming at low metallicity (Z_O/H <  0.1 Z_O/H⊙) in different mass ranges in the case with the environment-dependent IMF to that with the universal IMF as a function of redshift. The ratios are shown for the high metallicity extreme f_SFR(Z, z) from Chruslinska & Nelemans (2019) and for two non-universal IMF models from Jeřábková et al. (2018): IGIMF2 model – solid line; IGIMF3 model – dashed line. The large shaded area between the solid and dashed lines spans between the ratios obtained for these two IMF models. The ratios are also mildly affected by the conversion of 12 + log₁₀(O/H) to [Fe/H] metallicity measures. The thick solid and dashed curves were obtained for the default conversion described in Sect. 2. Using a conversion maintaining solar abundance ratios leads to a slight increase in the estimated ratios (thin lines, additional shadings).