Testing Moran's theorem in an agroecosystem

The abundance and reproductive effort of populations frequently fluctuate across space and time, a phenomenon known as spatial synchrony. Knowledge of the causes of this behavior underlies the ability to manage species, protect the health of humans and the environment, and increase agricultural sustainability. We used an agroecosystem to test Moran's theorem-spatial synchrony results from environmental entrainment. The controlled conditions of the agroecosystem allowed us to create a highly correlated environment while negating the effects of the alternative hypotheses: dispersal and trophic interactions. Under such conditions, synchrony of fruit production by 4288 trees was high over six years in a 32.5 ha pistachio orchard and occurred at similar temporal frequency as weather patterns demonstrating the Moran effect. The spatial synchrony of fruit production was less than the presumed synchrony of the environment supporting research from microcosms and observational studies showing the Moran effect is degraded by local mechanisms. Indeed even under the homogeneous environment of this system, synchrony declined significantly with distance among trees. We present evidence suggesting that the correlation of the local environment affects intrinsic dynamics to cause these patterns. Our findings demonstrate that the Moran effect is, at minimum, partially responsible for the synchronous fruit production in this system. Agroecosystems are often overlooked in basic ecological research; this experiment provides an example of their comparative advantages for the study of some ecological questions.