Spatial Scale of Population Synchrony: Environmental Correlation versus Dispersal and Density Regulation

Abstract

A stochastic model is developed to analyze the equilibrium spatial pattern of population synchrony, the correlation of temporal fluctuations in population density between localities. The expected population dynamics and the distribution of individual dispersal distance are homogeneous in space. Environmental stochasticity is caused by temporal fluctuations in the intrinsic rate of increase and/or carrying capacity of local populations that are correlated in space (but not time), the environmental correlation decreasing with distance. We analyze a linearized model for small fluctuations. Employing the standard deviation of a function in a given direction as a measure of scale, the spatial scale of population synchrony, lρ, is related to the spatial scales of environmental correlation, le, and individual dispersal, l, by the simple general formula $$l^{2}_{\rho }=l^{2}_{e}+ml^{2}/ \gamma $$ , where m is the individual dispersal rate and γ is the strength of population density regulation (or rate of return to equilibrium, $$\overline{r}$$ in the logistic model). Relative to environmental correlation (the Moran effect), the contribution of individual dispersal to the spatial scale of synchrony is magnified by the ratio of the individual dispersal rate to the strength of density regulation. Thus, even if the scale of individual dispersal is smaller than that of environmental correlation, dispersal can substantially increase the scale of population synchrony for weakly regulated populations.