Ecosystem stability (i.e., the inverse of variability of ecosystem function through time) is critical for maintaining ecosystem services and for preventing ecosystems from crossing catastrophic thresholds, such as the 1930s Dust Bowl in the US. Global change drivers (GCDs), such as eutrophication, droughts, floods, and changes in temperature, are likely to have substantial impacts on ecosystem stability. Local plant diversity has been found to be a key driver of stability at small spatial scales due in part to asynchrony among species abundances through time. However, global change drivers may alter heterogeneity of communities across space at larger scales (i.e., beta diversity), which may further influence ecosystem stability through two mechanisms. First, beta diversity may alter the synchrony among local communities through time because different local collections of species are likely to respond differently to interannual variation in environmental drivers. Second, beta diversity may cause different populations of the same species to be out of sync with one another because they are competing with different assemblages of species in different local communities.
We used a dataset containing 176 treatment-control pairs from 58 global change experiments around the world to address the following questions: (1) How do GCDs alter stability and its mechanisms at larger spatial scales (i.e., meta-community level)? (2) Are the direction and magnitude of GCD effects on stability related to ecosystem attributes (mean annual precipitation, mean annual temperature, regional richness)? (3) How do GCD effects on beta diversity relate to responses of stability of the system?
Results/Conclusions
Surprisingly, we found impacts of a variety of GCDs (nitrogen, phosphorus, multiple nutrients, irrigation, drought, warming) on stability centered at zero. Yet, within each GCD there was much unexplained variation – some experiments showed positive impacts on stability and others showed negative impacts. This variation was not related to site-level mean annual precipitation, mean annual temperature, or regional richness. However, we found that when GCDs altered beta diversity, this explained a large proportion of the variance in GCD effects on stability, with more beta diverse communities having greater stability. Using structure equation models, we determined that the mechanism responsible for this effect was that beta diversity decreased the synchrony among local populations, which ultimately stabilized the meta-community. As such, we suggest that maintenance of heterogeneity of landscapes will be critical for promoting the stability of populations and ecosystems, and that this may be just as important as maintaining local diversity.