Understanding the relationship between biodiversity and ecosystem functioning (BEF) is a central topic in ecology. Multi-traits based functional diversity has been proposed to improve mechanistic understanding of the BEF relationship; however, how trait-based functional diversity affects ecosystem functioning and processes has rarely been addressed in aquatic ecosystems.Here, we examined the causal relationship between three phytoplankton functional diversity indices (FAD2, FDc, FRic) and resource use efficiency for nitrogen (RUEN), phosphorus (RUEP), and silicate (RUESi), with monthly long-term datasets from the marine (Western English Channel, 2000 - 2014) and freshwater (Lake Kasumigaura, Japan, 1984 - 2012) ecosystem.We employed Convergent Cross Mapping (CCM), a novel method developed for identifying causality for nonlinear dynamical systems; this is in contrast to linear approaches that cannot distinguish causality from correlation.
Results/Conclusions
CCM found that FDc is the most robust functional diversity index in predicting phytoplankton resource use efficiency, and FDc has a much stronger causal strength on phytoplankton resource use efficiency than the Shannon index in both marine and freshwater ecosystem. Our study reveals the importance of functional diversity in understanding the biodiversity and ecosystem functioning relationship in aquatic ecosystems.