Both dispersal and the Moran effect significantly synchronized Tetrahymena fluctuations. However, the synchronizing effect of dispersal was much stronger in the presence of the predatory ciliate Euplotes patella. Analysis of a standard predator-prey model showed that predators enhanced the synchronizing effect of dispersal by generating predator-prey cycles. Ours is the first experimental demonstration of such 'phase locking' in a predator-prey system. We also explain why predator-prey cycles did not enhance the strength of the Moran effect. Our results suggest an explanation for why many of the most dramatic examples of spatial synchrony in nature involve species with cyclic dynamics.