  We performed Monte Carlo simulations of the symbiotic contact process on
different spatial dimensions ($d$). On the complete and random graphs (infinite
dimension), we observe hysteresis cycles and bistable regions, what is
consistent with the discontinuous absorbing-state phase transition predicted by
mean-field theory. By contrast, on a regular square lattice, we find no signs
of bistability or hysteretic behavior. This result suggests that the transition
in two dimensions is rather continuous. Based on our numerical observations, we
conjecture that the nature of the transition changes at the upper critical
dimension ($d_c$), from continuous ($d<d_c$) to discontinuous ($d>d_c$).
