Cumulative stellar-mass functions for the Fornax cluster (red lines) and IllustrisTNG Fornax-like groups (gray lines). The IllustrisTNG group most similar to Fornax is shown with the green lines. The different panels show the comparisons using different stellar-mass ranges: The upper panel shows galaxies with 6.5 < log(M_*/M_⊙) < 9, the middle panel shows galaxies between 7 < log(M_*/M_⊙) < 9, and the bottom panel shows galaxies with 8 < log(M_*/M_⊙) < 9.