  Synergistic and antagonistic interactions in multi-species populations - such
as resource sharing and competition - result in remarkably diverse behaviors in
populations of interacting cells, such as in soil or human microbiomes, or
clonal competition in cancer. The degree of inter- and intra-specific
interaction can often be quantified through the notion of an ecological
"niche". Typically, weakly interacting species that occupy largely distinct
niches result in stable mixed populations, while strong interactions and
competition for the same niche results in rapid extinctions of some species and
fixations of others. We investigate the transition of a deterministically
stable mixed population to a stochasticity-induced fixation as a function of
the niche overlap between the two species. We also investigate the effect of
the niche overlap on the population stability with respect to external
invasions. Our results have important implications for a number of experimental
systems.
