  We compare the properties of galaxy groups extracted from the Updated Zwicky
Catalogue (UZC) with those of groups extracted from N-body simulations of the
local Universe, in a LambdaCDM and a tauCDM cosmology. In the simulations, the
initial conditions of the dark matter density field are set to reproduce the
present time distribution of the galaxies within 80 Mpc/h from the Milky Way.
These initial conditions minimize the uncertainty originated by cosmic
variance, which has affected previous analyses of this small volume of the
Universe. The simulations also model the evolution of the photometric
properties of the galaxy population with semi-analytic prescriptions. The
models yield a galaxy luminosity function sensibly different from that of the
UZC and are unable to reproduce the distribution of groups and their luminosity
content. The discrepancy between the model and the UZC reduces substantially,
if we redistribute the luminosity among the galaxies in the simulation
according to the UZC luminosity function while preserving the galaxy luminosity
rank. The modified LambdaCDM model provides the best match to the UZC: the
abundances of groups by harmonic radius, velocity dispersion, mass and
luminosity are consistent with observations. We find that this model also
reproduces the halo occupation number of groups and clusters. However, the
large-scale distribution of groups is marginally consistent with the UZC and
the redshift-space correlation function of galaxies on scales larger than 6
Mpc/h is still more than 3-sigma smaller than observed. We conclude that
reproducing the properties of the observed groups certainly requires a more
sophisticated treatment of galaxy formation, and possibly an improvement of the
dark matter model.
