GC specific frequencies and galaxy mass densities define similar U-shape relations with M_V. Left: logarithm of the specific frequency, S_N, of GCs plotted vs. the host galaxy luminosity, M_V. The sample is taken from the compilation of Harris et al. (2013), but restricted to early-type galaxies (E/SO, dE/SO) for which dynamical mass estimates exist. We also indicate the mean S_N in bins of one magnitude (thick hexagons). Middle: logarithm of the projected 3D mass density within the half-light radius, ρ_3D, plotted vs. M_V for the same sample as in the left panel. The units of the mass density are pc ^-3. Right: survival fraction, f_S, of GCs with masses > after 10 Gyr of evolution plotted vs. the logarithm of the projected 3D mass density, ρ_3D, within the half-light radius of their host galaxy. The data are based on the simulations presented in Brockamp et al. (2014). The blue filled circles (fit by a solid blue line) correspond to the assumption of an isotropic GC velocity distribution, whereas the green filled circles (fit by a dashed green line) correspond to a modestly radially biased GC configuration. From the high to low survival fraction, the data correspond to the following template simulations: NGC 4889, VCC 1073, IC 1459, NGC 4494, and NGC 4564 (see also the summary in Table 1). The solid black curve shows the cumulative ρ_3D distribution of the sample of early type galaxies considered in the left and middle panels.