Environmental distances are more important than geographic distances when predicting spatial synchrony of zooplankton populations in a tropical reservoir

Abstract

Several studies have shown that spatial synchrony, which is defined as the strength of the correlation between time series, is a common pattern that occurs in different regions, types of ecosystems and groups of organisms. In addition to applied research (optimisation of monitoring networks and population persistence), spatial synchrony has important implications for unravelling the processes underlying environmental and biological dynamics. We quantified the levels of synchrony among six sites in a tropical reservoir (Lajes Reservoir, Rio de Janeiro, Brazil) over 85 months (from August 2001 to December 2009) for twelve environmental variables, four broad zooplankton groups (testate amoebae, rotifers, cladocerans and copepods) and 23 abundant taxa. We hypothesised that (a) environmental synchrony would be higher than biological synchrony; (b) high synchrony would be found; and (c) biological synchrony matrices would be positively correlated with environmental synchrony and negatively correlated with both environmental and geographic distances. A strong relationship between biological synchrony and environmental matrices, when compared to geographic distance, would be consistent with the hypothesis that similar environmental variability synchronises the dynamics of local populations (Moran effect). In comparison to previous studies, we found high levels of synchrony. Environmental synchrony was often higher than biological synchrony, which was in line with our expectation and previous findings. The high levels of synchrony found in this study suggest that reservoir zonation was not enough to desynchronise the dynamics at the sites for both environmental and biological variables. Spatial synchrony in zooplankton populations declined more consistently with environmental distance than with geographic distance. Additionally, environmental distances were unrelated to geographic distances. Taken together, these results indicate a preponderant role of the Moran effect. Thus, as synchrony increases extinction rates, we speculate that novel ecosystems may be highly susceptible to regional-wide changes in environmental factors.