Abundance of UDGs as a function of halo mass. Thick black points with errors: same as shown in Fig. 3, and these include the cluster points from vdB16. Black lines: best-fitting power-law relation including all black data points shown here. Blue squares: richnesses (i.e. the abundance of massive galaxies) in the same GAMA groups, with error bars defined in a similar way. Blue lines: best-fitting power-law relation to the richness points.