Occasional long-distance dispersal increases spatial synchrony of population cycles

1. Spatially-separated populations of the same species often exhibit correlated fluctuations in abundance, a phenomenon known as spatial synchrony. Dispersal can generate spatial synchrony. In nature, most individuals disperse short distances with a minority dispersing long distances. The effect of occasional long-distance dispersal on synchrony is untested, and theoretical predictions are contradictory. Occasional long-distance dispersal might either increase both overall synchrony and the spatial scale of synchrony, or reduce them.
2. We conducted a protist microcosm experiment to test whether occasional long-distance dispersal increases or decreases overall synchrony and the spatial scale of synchrony.
3. We assembled replicate 15-patch ring metapopulations of the protist predator Euplotes patella and its protist prey Tetrahymena pyriformis. All metapopulations experienced the same dispersal rate, but differed in dispersal distance. Some metapopulations experienced strictly short-distance (nearest neighbor) dispersal, others experienced a mixture of short- and long-distance dispersal.
4. Occasional long distance dispersal increased overall spatial synchrony and the spatial scale of synchrony for both prey and predators, though the effects were not statistically significant for predators. As predicted by theory, dispersal generated spatial synchrony by entraining the phases of the predator-prey cycles in different patches, a phenomenon known as phase locking.
5. Our results are consistent with theoretical models predicting that occasional long-distance dispersal increases spatial synchrony. However, our results also illustrate that the spatial scale of synchrony need not match the spatial scale of the processes generating synchrony. Even strictly short-distance dispersal maintained high spatial synchrony for many generations at spatial scales much longer than the dispersal distance, thanks to phase locking.