Population synchrony and environmental variation: an experimental demonstration

Understanding the causes of population synchrony is an important issue for population management. Its study in field populations involves disentangling the effects of dispersal and correlated environmental noise. Here we report on an experimental investigation of the synchronizing effects of noise in closed laboratory populations of a soil mite, Sancassania berlesei. Mite life-histories are highly plastic with respect to resource availability (which is a function of food supply and population density). By varying the food supply we imposed environmental variation. We show that (a) population synchrony is a function of environmental synchrony, (b) perceived population synchrony depends on the life-history stage counted, and (c) average population synchrony tends to be lower than environmental synchrony: even when populations were supplied with food with a correlation of 1.0, the correlation between populations was 0.63 (bootstrapped 95%CI 0.54-0.71). This supports recent theoretical work suggesting that the Moran theorem (indicating that population synchrony equals environmental synchrony) generally overestimates the population synchrony of nonlinear systems.