First experimental demonstration of spatially-synchronous predator-prey dynamics via phase locking

Background/Question/Methods

Spatially segregated populations of the same or similar species often fluctuate synchronously in nature. Three processes can generate spatial synchrony: i) dispersal of individuals between populations; ii) spatially synchronous fluctuations in exogenous environmental factors (the Moran Effect); and iii) interactions with other species (e.g. predators) which are themselves synchronized. All three processes co-occur in nature, making it difficult to tease apart their effects and quantify the synergies between them. In particular, species interactions may alter the impact of dispersal by generating population cycles, which theory suggests can be synchronized by very weak dispersal, an effect known as 'phase locking'. We manipulated the presence/absence of all three causes of spatial synchrony in a protist microcosm experiment using a fully-crossed factorial design and examined their effects on the synchrony of the dynamics of the ciliate prey species Tetrahymena pyriformis.

Results/Conclusions

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.

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