Population spatial synchrony, in which population fluctuations are correlated through time across multiple locations, is a ubiquitous and fundamental aspect of population ecology. Community ecology has emphasized a different kind of synchrony, i.e., whether temporal fluctuations of multiple species in a community are correlated. Both population spatial synchrony and community synchrony have major implications for ecosystem stability, but spatial synchrony has rarely, if ever, been applied to community attributes like species richness. In addition, given the strong links between biodiversity and the stability of ecosystem function, spatial synchrony in species richness could have profound effects on ecosystem stability and our ability to conserve and restore biodiversity. Here, we integrate insights from a theoretical model with a synthesis of 15 empirical metacommunities from terrestrial grassland and coastal marine biomes to address the following questions: 1) Do local fluctuations in richness exhibit spatial synchrony across metacommunity patches? 2) Are the well-documented drivers of population spatial synchrony (i.e., Moran effects and dispersal) also key drivers of spatial synchrony in richness? 3) Does the spatial synchrony of richness depend on the degree of niche differentiation among species in the community? 4) Does the strength of spatial synchrony of richness predict ecosystem stability?
Results/Conclusions
We quantified spatial synchrony of species richness in 15 empirical and over 2000 simulated metacommunities, by measuring the species richness of each plot at each point in time, and taking the average of all pairwise Spearman correlations among richness time series for individual plots. Species richness was spatially synchronous in theory and data; empirical synchrony values spanned ca. 0.05 to 0.8 (median ca. 0.4) and were in all cases significantly different from a null hypothesis of no spatial synchrony (p< 0.05). Sensitivity analyses performed on theoretical simulation data showed that dispersal and Moran effects are the key processes that produce spatial synchrony of species richness, mirroring mechanisms from population synchrony. In both theoretical and empirical metacommunities, higher species richness yielded greater spatial synchrony in richness. Assuming that, all else being equal, more species rich communities have greater niche overlap, this finding suggests that the degree of niche differentiation partly controls spatial synchrony in richness. Moreover, synchrony in richness was negatively correlated with ecosystem stability in theory and empirical data. The spatial synchrony of community properties is a potential new lens into the spatiotemporal dynamics of communities and their implications for system stability.