Spatially autocorrelated disturbances and patterns in population synchrony

Spatially synchronous population dynamics have been documented in many taxa . The prevailing view is that the most plausible candidates to explain this pattern are extrinsic disturbances (the Moran effect) and dispersal. In mo st cases disentangling these factors is difficult. Theoretical studies have shown that dispersal between subpopulations is more likely to produce a ne gative relationship between population synchrony and distance between the p atches than perturbations. As analyses of empirical data frequently show th is negative relationship between the level of synchrony and distance betwee n populations, this has emphasized the: importance of dispersal as a synchr onizing agent. However, several weather patterns show spatial autocorrelati on, which could potentially produce patterns in population synchrony simila r to those caused by dispersal. By using spatially extended versions of sev eral population dynamic models, we show that this is indeed the case. Our r esults show that, especially when both factors (spatially autocorrelated pe rturbations and distance-dependent dispersal) act together, there may exist groups of local populations in synchrony together but fluctuating asynchro nously with some other groups of local populations. We also show, by analys ing 56 long-term population data sets, that patterns of population synchron y similar to those found in our simulations are found in natural population s as well. This finding highlights the subtlety in the interactions of disp ersal and noise in organizing spatial patterns in population fluctuations.