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PubMed · 10777435

Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics.

Abstract

Many species exhibit widespread spatial synchrony in population fluctuations. This pattern is of great ecological interest and can be a source of concern when the species is rare or endangered. Both dispersal and spatial correlations in the environment have been implicated as possible causes of this pattern, but these two factors have rarely been studied in combination. We develop a spatially structured population model, simple enough to obtain analytic solutions for the population correlation, that incorporates both dispersal and environmental correlation. We ask whether these two synchronizing factors contribute additively to the total spatial population covariance. We find that there is always an interaction between these two factors and that this interaction is small only when one or both of the environmental correlation and the dispersal rate are small. The interaction is opposite in sign to the environmental correlation; so, in the normal case of positive environmental correlation across sites, the population synchrony will be lower than predicted by simply adding the effects of dispersal and environmental correlation. We also find that population synchrony declines as the strength of population regulation increases. These results indicate that dispersal and environmental correlation need to be considered in combination as explanations for observed patterns of population synchrony.

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BibTeXRIS

Bruce E Kendall, Ottar N Bjørnstad, Jordi Bascompte, Timothy H Keitt, William F Fagan. 2000. Dispersal, Environmental Correlation, and Spatial Synchrony in Population Dynamics.. https://doi.org/10.1086/303350

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

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 [Formula: see text], where m is the individual dispersal rate and γ is the strength of population density regulation (or rate of return to equilibrium, [Formula: see text] 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.

Moran effect↗