  We use imaging from the Next Generation Virgo cluster Survey (NGVS) to
present a comparative study of ultra-compact dwarf (UCD) galaxies associated
with three prominent Virgo sub-clusters: those centered on the massive,
red-sequence galaxies M87, M49 and M60. We show how UCDs can be selected with
high completeness using a combination of half-light radius and location in
color-color diagrams ($u^*iK_s$ or $u^*gz$). Although the central galaxies in
each of these sub-clusters have nearly identical luminosities and stellar
masses, we find large differences in the sizes of their UCD populations, with
M87 containing ~3.5 and 7.8 times more UCDs than M49 and M60, respectively. The
relative abundance of UCDs in the three regions scales in proportion to
sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number
of globular clusters, and number of nearby galaxies. We find that the UCDs are
predominantly blue in color, with ~85% of the UCDs having colors similar to
blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs
surrounding M87 and M49 may follow a morphological sequence ordered by the
prominence of their outer, low surface brightness envelope, ultimately merging
with the sequence of nucleated low-mass galaxies, and that envelope prominence
correlates with distance from either galaxy. Our analysis provides evidence
that tidal stripping of nucleated galaxies is an important process in the
formation of UCDs.
