  Galaxy formation inside dark matter halos, as well as the halo formation
itself, can be affected by large-scale environments. Evaluating the imprints of
environmental effects on galaxy clustering is crucial for precise cosmological
constraints with data from galaxy redshift surveys. We investigate such an
environmental impact on both real-space and redshift-space galaxy clustering
statistics using a semi-analytic model derived from the Millennium Simulation.
We compare clustering statistics from original SAM galaxy samples and shuffled
ones with environmental influence on galaxy properties eliminated. Among the
luminosity-threshold samples examined, the one with the lowest threshold
luminosity (~0.2L_*) is affected by environmental effects the most, which has a
~10% decrease in the real-space two-point correlation function (2PCF) after
shuffling. By decomposing the 2PCF into five different components based on the
source of pairs, we show that the change in the 2PCF can be explained by the
age and richness dependence of halo clustering. The 2PCFs in redshift space are
found to change in a similar manner after shuffling. If the environmental
effects are neglected, halo occupation distribution modeling of the real-space
and redshift-space clustering may have a less than 6.5% systematic uncertainty
in constraining beta from the most affected SAM sample and have substantially
smaller uncertainties from the other, more luminous samples. We argue that the
effect could be even smaller in reality. In the Appendix, we present a method
to decompose the 2PCF, which can be applied to measure the two-point
auto-correlation functions of galaxy sub-samples in a volume-limited galaxy
sample and their two-point cross-correlation functions in a single run
utilizing only one random catalog.
