Spatial synchrony in the dynamics of moth and aphid populations

1. We report patterns of intraspecific spatial synchrony (cross-correlation with lag zero) in the dynamics of British moths and aphids sampled at 57 and 21 localities throughout the UK. 2. Spatial synchrony was substantially higher in aphids than in moths. In both taxa, spatial synchrony declined with increasing distance between conspecific populations, but synchrony remained positive at all distances up to 800 km. 3. Species with large slopes (>2) of the spatial variance-mean regression had spatially asynchronous dynamics, as predicted by a theoretical model. 4. In noctuid moths and in aphids, but not in geometrid moths, there was a significant positive correlation between the degree of spatial synchrony and the level of temporal variability in local populations. 5. We discuss the two main hypotheses about the causes of spatial synchrony, migration and regional stochasticity (spatially correlated weather conditions). We conclude that our results on large-scale spatial synchrony in moths and aphids are better explained by regional stochasticity than by migration.