[C01] Ecology and Enviromment

[C01-02] Functional coexistence theory: predicting ecosystem outcomes from coexistence mechanisms

Joe Wan^1,2, *Po-Ju Ke², Iris Hordijk^1,3, Lalasai Bialic-Murphy¹, Thomas W Crowther¹ (1. Institute of Integrative Biology, ETH Zurich (Switzerland), 2. Institute of Ecology and Evolutionary Biology, National Taiwan University (Taiwan), 3. Forest Ecology and Forest Management Group, Wageningen University & Research (Netherlands))

Keywords:

Species coexistence,Modern coexistence theory,Biodiversity-ecosystem functioning,overyielding,Niche and fitness differences

Understanding how biodiversity influences ecosystem functioning (e.g., biomass production) remains a central challenge in ecology. Although empirical studies often show that more diverse communities produce more biomass (i.e., overyielding), the underlying mechanisms are not fully understood. In community ecology, modern coexistence theory provides a framework for understanding how niche and fitness differences contribute to species coexistence. Here, we present an extension of the theoretical framework, which we term functional coexistence theory, that integrates concepts from modern coexistence theory to explain how the coexistence of species shapes total community function. We derive mathematical conditions showing that overyielding in biomass production occurs when niche and fitness differences are in excess of what is needed for coexistence. Specifically, our framework identifies three key components. First, niche differences that stabilize coexistence also contribute positively to ecosystem function. Second, species that contribute more to function should also possess higher competitive fitness. Third, reducing differences in intrinsic yield among species (i.e., functional equalization) increases the potential for overyielding. Using a resource competition model, we show that our theory applies to multi-species communities. We also demonstrate the empirical relevance of our analytical framework by fitting the model to data from a classic plant competition experiment. In conclusion, our framework provides a mathematical foundation for linking community composition to ecosystem-level outcomes and opens new directions for modeling biodiversity–function relationships.