Spatially‐nested topologies stabilize meta‐ecosystems via cross‐scale source‐sink dynamics

Ecosystems are open to spatial flows of nonliving resources and dispersing organisms that can interact to drive their dynamics and functions. Empirical evidence shows resource flows and dispersal commonly have contrasting properties: resource flows connect nearby ecosystems of different types, while dispersal connects relatively distant ecosystems of similar types. For instance, islands and adjacent coral reefs are connected through resource exchanges but also exhibit organisms that disperse across larger spatial scales between homologous ecosystems. These contrasting properties of spatial flows can yield spatially nested topologies of diverse, coupled ecosystems, where nearby ecosystems coupled via resource flows are embedded within larger scale dispersal networks. Using meta-ecosystem models, we show that spatially nested topologies of coupled ecosystems have a general stabilizing effect on ecosystem dynamics. Stabilization results from the emergence of cross-scale source-sink dynamics, where some ecosystems act as nutrient sources but consumer sinks and others as nutrient sinks but consumer sources-creating a self-regulating spatial structure that dampens local instabilities. These dynamics lead to spatial variation in trophic regulation and biomass stocks across ecosystems of the same type: consumer sinks exhibit stronger top-down control and lower primary producer stocks, while consumer sources exhibit stronger bottom-up control and higher producer stocks. These local effects of cross-scale source-sink dynamics scale up to influence functions at the meta-ecosystem scale, including increasing primary production and nutrient retention. Critically, we further demonstrate how these source-sink dynamics depend on the dispersal rates of consumer species in both ecosystem types, such that the stability and function of one ecosystem type can be shaped by the dispersal rate of consumers in another. Our findings suggest that the diversity of ecosystem types and the hierarchy of spatial flow scales observed ubiquitously in nature are key properties of spatial ecological systems, driving their stability and functions across scales.