Background/Question/Methods It is well known that the degree of synchrony of the dynamics of multiple populations heavily modifies the degree of variability, through time, of any ecosystem function or other quantity which depends in an aggregate manner on the populations. For instance, the variability through time of the total biomass of forage in a pasture depends strongly on the degree of synchrony between the abundance fluctuations of distinct plant species in the pasture, with asynchrony tending to promote temporal stability of total biomass and synchrony tending to produce instability. Past research on links between population variability, synchrony, and variability of ecosystem functioning usually assessed synchrony using simple correlation or covariance statistics and usually assessed variability of ecosystem functioning using the coefficient of variation or a related measure. But recent research shows that both synchrony of populations and variability of an ecosystem function are statistically complex phenomena. Taking into account new statistical aspects of these phenomena can illuminate new dimensions of ecosystem stability which are important both for basic understanding and for applications.
Results/Conclusions After introducing the Symposium of which this talk is part, I will briefly review time- and timescale-specific and geographic approaches to synchrony and their benefits for understanding ecosystem stability across scales. I will then focus on recent results on “asymmetric tail associations” (ATAs) between population time series and their importance for ecosystem stability. Two partially synchronous population time series are considered asymmetrically tail associated if they are more strongly associated when the species are relatively common than when they are relatively scarce, or vice versa. ATAs are common between populations within communities and metacommunities. ATAs can influence the stability of ecosystem functions of both metapopulations and local communities. ATAs can accentuate the extinction risk of metapopulations. ATAs can alter species competition, sometimes making the difference between species coexistence and competitive exclusion. In all these ways, ATAs are a novel statistical aspect of the synchrony of populations which can make a major difference for ecosystem stability, on multiple scales and in multiple contexts. We present both new theory and new statistics, and draw on examples from grassland, aphid, plankton, and kelp forest metapopulations and metacommunities.
