Specific frequency of UCDs. The large filled circles with error bars indicate the UCD specific frequency S_N,UCD as derived in the text for six different environments. These are, from bright to faint host galaxy luminosities: Centaurus, Fornax, Hydra, HCG90, HCG22, Local Group. See also Table 1. Large magenta circles are the GC specific frequencies S_N,GC in the investigated environments, see text for details – estimates for the HCGs are not available. Small (green) dots are literature GC specific frequencies S_N,GC over a range of environments (Dirsch et al. 2003; Mieske et al. 2005; Peng et al. 2008 and references therein). The dashed arrow for HCG90 indicates the location of this data point if the 35% intragroup light component (see text) would not be considered for the total luminosity.