Functional community structure modulates zooplankton production rates across boreal lakes

Although there is a general consensus in ecology that more diverse communities tend to be more productive, it is still unclear whether this holds for aquatic ecosystems, especially with indicators of productivity rates and not just standing biomass proxies. Furthermore, most evidence is based on the results of experimental studies in which biodiversity was assessed through taxonomic richness, although functional indicators could be more relevant. Consequently, we still have a poor understanding of how real community performance is linked to the various features of community structure in natural aquatic ecosystems. Here we explicitly assessed the effect of functional traits and diversity on crustacean zooplankton productivity rates measured across 84 boreal Canadian lakes spanning wide limnological gradients. Productivity was assessed using the chitobiase enzyme method. Redundancy analyses and structured equation modelling were used to assess the relationship between zooplankton production rates, community structure (diversity and functional composition), while accounting for standing biomass and environmental factors After controlling for the effect of environmental factors, zooplankton production rates were positively linked to dominance (lower functional evenness) by certain feeding traits (Daphnia filtration and Chydorus filtration), demonstrating an identity (selection) effect. Overall, the magnitude of the functional compositional effect on production was comparable to the aggregate effect of the environmental variables. Our study demonstrates that zooplankton functional community structure plays an important role in the regulation of a pivotal lake ecosystem function.