On the structure of species-function participation in multilayer ecological networks

Understanding how biotic interactions shape ecosystems and impact their functioning, resilience, and biodiversity has been a key research focus in ecology. Traditional assessments of ecological complexity typically focus on species-species interactions that mediate a particular ecological function, overlooking the synergistic effects that multiple functions might develop and the resulting species-function participation patterns that emerge in multifunctional ecosystems. We propose to integrate various biotic interactions between species into a resource-consumer-function tensor, visualized as a multilayer network. Adequately projecting the tensor allows to quantify how species and functions are intertwined and to leverage indirect effects to identify key actors.

Applying this framework to recent data from an islet ecosystem unveils a non-random, nested structure in plant species' participation across functions. Such structure suggests a participation-based ranking of species and functions, confirmed by considering indirect connections between species and functions. These rankings identify a subset of woody shrubs as keystone species and decomposition as a keystone function, whose removal have a larger-than-random effect on secondary extinctions. Overall, the dual insight that this framework offers opens the door to a richer quantification of ecosystem complexity and to better calibrate the influence of multifunctionality on ecosystem functioning and biodiversity.