Linking zooplankton communities to ecosystem functioning: toward an effect-trait framework

The renewed interest in trait-based approaches has offered a stimulating, conceptual framework for predicting species distributions, assessing community composition and determining biodiversity-ecosystem linkages. However, despite previous attempts to clarify trait terminology and its application, selecting ecologically meaningful traits that mechanistically link levels of biological organization remains a challenge in aquatic ecology. Response traits can be used to capture community assembly processes along environmental gradients, while effect traits hold the potential to predict ecosystem functions. Although effect traits related to organismal physiology and body composition best allow for extrapolation from individuals to ecosystem processes, such traits are still rarely incorporated within plankton functional approaches or classifications for numerous reasons. Synthesizing current knowledge on effect traits in zooplankton, we call for a better implementation of such metrics as descriptors of community structure. We then capitalize on concepts of bioenergetics and ecosystem ecology to propose a hierarchical framework for zooplankton trait classification, identifying key traits fulfilling organismal functions and linking these to ecosystem processes likely to be influenced. Our framework provides insight regarding trait trade-offs, with implications for feedbacks to ecosystems, aiming to bridge the gap between plankton community ecology and aquatic biogeochemistry.