Dispersal increases spatial synchrony of populations but has weak effects on population variability: a meta-analysis

The effects of dispersal on spatial synchrony and population variability have been well documented in theoretical research, and a growing number of empirical tests have been performed. Yet a synthesis is still lacking. Here, we conducted a meta-analysis of relevant experiments and examined how dispersal affected spatial synchrony and temporal population variability across scales. Our analyses showed that dispersal generally promoted spatial synchrony, and such effects increased with dispersal rate and decreased with environmental correlation among patches. The synchronizing effect of dispersal, however, was only detected when spatial synchrony was measured using the correlation-based index, but not for the covariance-based index. In contrast to theoretical predictions, the effect of dispersal on local population variability was generally non-significant, except when environment correlation among patch was negative and/or experimental period was long. At the regional scale, while low dispersal stabilized metapopulation dynamics, high dispersal led to destabilization. Overall, the sign and strength of dispersal effects on spatial synchrony and population variability were modulated by taxa, environmental heterogeneity, type of perturbations, patch number, and experimental length. Our synthesis demonstrates that dispersal can substantially affect the dynamics of spatially distributed populations, but its effects are context dependent on abiotic and biotic factors.