Global patterns of environmental synchrony and the Moran effect

There is considerable debate over the relative importance of dispersal and environmental disturbances (the Moran effect) as causes of spatial synchrony in fluctuations of animal populations. If environmental factors generally exhibit high levels of spatial autocorrelation, they may be playing a more important role in synchronizing animal populations than sometimes recognized. Here I examine this issue by analyzing spatial autocorrelation in annual rainfall and mean annual temperatures from sites throughout the world using the database maintained by the Global Historical Climatology Network. Both annual precipitation and mean annual temperatures exhibit high synchrony declining with distance and are statistically significant over large distance, often on a continental scale. In general, synchrony was slightly higher in annual precipitation at short distances, but greater in mean annual temperatures at long distances. No latitudinal gradient in synchrony of either variable was detected. The high overall synchrony observed in these environmental variables combined with a pattern of decline with distance similar to that observed in many animal populations suggest that the Moran effect can potentially play an important role in driving synchrony in a wide variety of ecological phenomena regardless of scale.