Linking species coexistence and ecosystem functioning in model metacommunities

Theories of species coexistence and biodiversity-ecosystem functioning relationships (BEF) provide fundamental frameworks for understanding the maintenance of biodiversity and its functional consequences, respectively. While coexistence and BEF are intrinsically linked through shared underlying drivers and processes, they are usually studied separately, hindering an integrative understanding of the causes and consequences of biodiversity. In this study, we examine the relationships between coexistence potential and BEF in heterogeneous metacommunities. By developing a spatially implicit metacommunity model, we investigate how spatial processes (e.g., spatial heterogeneity, dispersal) and interspecific traits (e.g., interspecific niche differentiation, asymmetry) influence species coexistence potential and BEF. Coexistence potential is defined as the average invasion growth rate of species at low density and is decomposed into non-spatial fitness, spatial storage effects, and fitness-density covariance. BEF is quantified as the difference between mixture yield and mean monoculture yield and partitioned into average complementarity, average selection, and spatial selection effects. By combining analytical investigations and simulations, we explore how spatial and interspecific drivers regulate these components, thereby mediating the coexistence-BEF relationships.

Under certain assumptions, analytical solutions show that increased spatial heterogeneity and reduced dispersal promote both species coexistence and BEF in metacommunities by increasing the spatial storage effect, fitness-density covariance, spatial selection effect and average complementarity effect, yielding a positive coexistence–BEF correlation. The relative contribution of each component to the overall variation of coexistence potential and BEF varies with dispersal rate, which also governs how component-level covariation shapes their correlation. Simulations along gradients of niche differentiation and asymmetry show that niche differentiation promotes coexistence and BEF by enhancing non-spatial fitness and average complementarity, while interspecific asymmetry contributes primarily through increasing average selection effects. Our simulations confirm a generally positive coexistence-BEF correlation, including scenarios with non-random dispersal, etc. That said, negative correlations between coexistence potential and BEF may also occur, such as in metacommunities with competition-colonization trade-offs. Overall, our analyses demonstrate that in metacommunities, coexistence and BEF are often positively correlated, mediated by shared spatial and interspecific drivers. Our findings bridge the gap between coexistence and BEF across spatial scales, offering new insights into how spatial processes shape biodiversity and ecosystem functioning.