Changes in large-scale climate alter spatial synchrony of aphid pests

Spatial synchrony, the tendency of distant populations to fluctuate similarly, is a major concern in ecology(1-8). Except in special circumstances(3,9), researchers historically had difficulty identifying drivers of synchrony in field systems(5,6,10). Perhaps for this reason, the possibility(9,11,12) that changes in large-scale climatic drivers may modify synchrony, thereby impacting ecosystems and human concerns, has been little examined. Here, we use wavelets to determine environmental drivers of phenological synchrony across Britain for 20 aphid species, most major crop pests. Consistently across species, changes in drivers produced large changes in aphid synchrony. Different drivers acted on different timescales: using a new wavelet analogue of the Moran theorem(1), we show that on long timescales (>4 years), 80% of synchrony in aphid first flights is due to synchrony in winter climate; but this explanation accounts for less short-timescale (<= 4 years) synchrony. Changes in aphid synchrony over time also differed by timescale: long-timescale synchrony fell from before 1993 to after, caused by similar changes in winter climate; whereas short-timescale synchrony increased. Shifts in winter climate are attributable to the North Atlantic Oscillation, an important climatic phenomenon(7,11,13), so effects described here may influence other taxa. This study documents a new way that climatic changes influence populations, through altered Moran effects.