Diversity-stability relationships across spatial scales: Aggregate and compositional variability correlate with different dimensions of metacommunity diversity

Nathan Wisnoski, University of Wyoming and Eric R. Sokol, Batelle, National Ecological Observatory Network (NEON), Boulder, CO

Background/Question/Methods
Temporal stability (or variability) of the distribution and abundance of species has important implications for the maintenance of biodiversity and ecosystem functions. In ecological communities, temporal stability can be quantified with respect to multiple dimensions of diversity, including composition as well as the stability of aggregate properties, such as total community abundance or biomass. The spatial scaling of stability in metacommunities is jointly influenced by local community dynamics and their degree of spatial synchrony. The degree of synchrony observed in such a system can be strongly influenced by connectivity, characterized by dispersal and colonization dynamics. Temporal stability in aggregate community properties, such as total biomass, typically increases with local diversity and is increased at the metacommunity scale by spatially asynchronous fluctuations. But aggregate properties mask underlying changes in community composition. It is unclear how aggregate and compositional stability jointly scale with biodiversity. Here, we evaluate the spatial scale dependence of diversity-stability relationships using community data collected across the diverse ecosystems of the U.S. Long-Term Ecological Research (LTER) Network. Specifically, we examine community stability (1/variability) using both aggregate and compositional measures at local and regional spatial scales and compare relative strengths of spatial stabilization.
Results/Conclusions
Across the broad range of ecosystems and organisms examined in this study, including algae, birds, corals, fishes, herptiles, plants, marine invertebrates, freshwater macroinvertebrates, and zooplankton, we found both aggregate and compositional measures of community structure were more stable when quantified at larger (e.g., regional) spatial scales. However, the relative stability of total abundance versus composition due to spatial processes was highly variable among data sets, suggesting different levels of importance for inter-patch connectivity for different metacommunity types. We found measures of total metacommunity abundance were most stable in metacommunities with higher beta-diversity, while measures of metacommunity compositional stability decreased with increasing alpha- and gamma-diversity. Overall, our study suggests that local diversity-stability relationships may become decoupled at larger spatial scales. Thus, while the destabilizing effects of diversity on community composition scale across space, the stabilizing effect of diversity on aggregate properties shifts from being driven by alpha-diversity at local scales to beta-diversity at larger scales, where spatial asynchrony plays a larger role in conferring stability. Importantly, we demonstrate key differences in how stability changes across scales and how changes in stability are related to different dimensions of diversity in metacommunities.