Biodiversity effects on ecological stability through ecosystem-level feedback

Portfolio mechanisms are widely recognized as essential processes through which biodiversity promotes ecosystem stability. However, traditional theories often treat biodiversity as a static property, overlooking its dynamic nature, which is shaped by numerous ecosystem-level processes identified since the 1950s. To address this gap, we develop a novel model framework grounded in island biogeography theory (IBT) to explore the ecosystem-level mechanisms by which biodiversity and its dynamics influence ecosystem stability. This framework considers species diversity as a state variable, capturing its dynamical behavior driven by feedback mechanisms between species diversity, resource availability (nutrients), and the effects of diversity on multitrophic interactions within a plankton system. Specifically, our model demonstrates that phytoplankton diversity regulates the strength of plankton trophic interactions, which in turn alter plankton biomass and nutrient availability. These changes generate feedback loops that further reshape phytoplankton diversity itself. The presence of the feedback loops enhances the system's resistance to extinction: Increasing diversity promotes more efficient resource consumption when consumers face extinction risk, while declining diversity reduces resource consumption efficiency, thereby mitigating destabilization caused by consumer overgrazing. The critical role of species diversity dynamics in ecosystem stability is empirically supported by our analysis of a 30-year phytoplankton dataset, which reveals a causal relationship between temporal variability in phytoplankton species richness and the stability of community biomass. Our findings unveil a new mechanism through which biodiversity influences ecosystem stability via ecosystem-level processes, independently of population- or community-level portfolio processes.