Although diversity–stability relationships have been extensively studied in local ecosystems, the global biodiversity crisis calls for an improved understanding of these relationships in a spatial context. Biodiversity is not only declining in many local ecosystems, but is also becoming increasingly homogenised across space. It remains unclear how biotic homogenisation may affect the dynamics and stability of ecosystems at landscape to regional scales.
In our study, we develop a general theoretical framework to understand ecosystem stability at multiple scales. Based on this framework, we use a dynamical model of competitive metacommunities to study the relationships between species diversity and ecosystem variability across scales. Our model is a simple extension of the Lotka–Volterra competition model in a patchy, stochastic environment. We derive analytic relationships under a limiting case; these results are extended to more general cases with numerical simulations.
Results/Conclusions
We developed a spatial partitioning framework to understand the stability and variability of ecosystems across scales. Analogously to the partitioning of biodiversity, we propose the concepts of alpha, beta and gamma variability. Gamma variability at regional (metacommunity) scale can be partitioned into local alpha variability and spatial beta variability, either multiplicatively or additively. On average, variability decreases from local to regional scales, which creates a negative variability–area relationship.
Our dynamical model shows that, while alpha diversity decreases local ecosystem variability, beta diversity generally contributes to increasing spatial asynchrony among local ecosystems. Consequently, both alpha and beta diversity provide stabilising effects for regional ecosystems, through local and spatial insurance effects respectively. We further show that at the regional scale, the stabilising effect of biodiversity increases as spatial environmental correlation increases. Our findings have important implications for understanding the interactive effects of global environmental changes (e.g. environmental homogenisation) and biodiversity loss on ecosystem sustainability at large scales.