  An ensemble cluster has been formed from a data set comprising a complete
magnitude-limited sample of 680 giant galaxies (M(B) < -19) in 8 low-redshift
clusters, normalised by the velocity dispersions and virial radii for the
early-type cluster populations. Distinct galaxy populations have been
identified, including an infall population. A majority (50-70% or greater) of
the infall population are found to be in interacting or merging systems
characterised by slow gravitational encounters. The observed enhancement of
galaxy-galaxy encounters in the infall population compared to the field can be
explained by gravitational shocking. It is shown that disc galaxy mergers in
the infall population integrated over the estimated lifetime of the cluster (~
10 Gyr) can readily account for the present cluster S0 population.
