  Ultra-compact dwarf galaxies (UCDs) are predominatly found in the cores of
nearby galaxy clusters. Besides the Fornax and Virgo cluster, UCDs have also
been confirmed in the twice as distant Hydra I and Centaurus clusters. Having
(nearly) complete samples of UCDs in some of these clusters allows the study of
the bulk properties with respect to the environment they are living in.
Moreover, the relation of UCDs to other stellar systems in galaxy clusters,
like globular clusters and dwarf ellipticals, can be investigated in detail
with the present data sets. The general finding is that UCDs seem to be a
heterogenous class of objects. Their spatial distribution within the clusters
is in between those of globular clusters and dwarf ellipticals. In the
colour-magnitude diagram, blue/metal-poor UCDs coincide with the sequence of
nuclear star clusters, whereas red/metal-rich UCDs reach to higher masses and
might have originated from the amalgamation of massive star cluster complexes
in merger or starburst galaxies.
