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.