Population synchrony in temporally and spatially correlated environments: Environmental colour enhances the Moran effect

Evidence for synchronous fluctuations of spatially separated populations is ubiquitous in the literature, including accounts within and across taxa. Among the few mechanisms cited to explain this phenomenon is the Moran effect which suggests that the degree of population synchrony is equivalent to the degree of climate synchrony between the habitats. The theory underlying the Moran effect relies upon the assumption that climate fluctuations within a habitat are temporally (serially) uncorrelated. While recent analyses have shown that many environmental variables possess strong temporal autocorrelation (known also as ‘colour’), the impact of coloured noise upon Moran effects are poorly understood, possibly due to the lack of numerical methods capable of generating coloured cross-correlated noises. Here I present a novel and simple method to generate such noises and I investigate their impact on population synchrony. For linear and non-linear population dynamics, coloured environments strengthen the association between the environmental and population cross-correlation when populations differ in their density dependencies. Given that most environmental variables are moderately coloured, these results imply that the Moran effect may be a far more significant driver of regional-scale synchrony than is currently believed.