Root mean square of as a functionof the dust-to-gas density ratio ρ_d∕ρ_g. The orange, green, and purple lines represent the turbulent strength in simulations in which we initialize the dust after the vertical shear instability has saturated. The strength at low to intermediate values of the volume density ratio in the three simulations is marginally smaller if the dust-to-gas surface density ratio is greater. Nevertheless, the Mach number is higher in all of these simulations than in the simulation in which we introduce the dust at the start (blue line). We find that the stronger turbulence in the former simulations is driven by the vertical shear instability, while the weaker turbulence in the latter one is caused by the streaming instability. Independent of the source of the turbulence, its strength decreases at dust densities larger than the gas density in all four simulations.