Spatial synchrony propagates through a forest food web via consumer-resource interactions.

In many study systems, populations fluctuate synchronously across large regions. Several mechanisms have been advanced to explain this, but their importance in nature is often uncertain. Theoretical studies suggest that spatial synchrony initiated in one species through Moran effects may propagate among trophically linked species, but evidence for this in nature is lacking. By applying the nonparametric spatial correlation function to time series data, we discover that densities of the gypsy moth, the moth's chief predator (the white-footed mouse), and the mouse's winter food source (red oak acorns) fluctuate synchronously over similar distances (approximately1000 km) and with similar levels of synchrony. In addition, we investigate the importance of consumer-resource interactions in propagating synchrony among species using an empirically informed simulation model of interactions between acorns, the white-footed mouse, the gypsy moth, and a viral pathogen of the gypsy moth. Our results reveal that regional stochasticity acting directly on populations of the mouse, moth, or pathogen likely has little effect on levels of the synchrony displayed by these species. In contrast, synchrony in mast seeding can propagate across trophic levels, thus explaining observed levels of synchrony in both white-footed mouse and gypsy moth populations. This work suggests that the transfer of synchrony among trophically linked species may be a major factor causing interspecific synchrony.