When form does not predict function: empirical evidence violates functional form hypotheses for marine macroalgae

1) Functional groups are widely used to reduce complexity and generalize across ecological communities. These models assume that shared traits among species correspond to some ecological role, process, or function, and that these traits can be leveraged to generate meaningful and distinct functional groups so that intergroup trait variation exceeds intragroup variation.

2) We sought to validate the assumptions of the widely used Functional Group Model (FGM) for marine macroalgae, which groups species based on morphological complexity, by testing the predictions of the FGM for several traits assumed to correspond with morphological complexity. The FGM predicts increased resistance to disturbance and herbivory as morphological complexity (tensile strength and thallus toughness, respectively) increases. The FGM also predicts a tradeoff between complexity and growth rate. To test predictions, we measured: 1) thallus toughness (force to penetrate), 2) tensile strength (force to break) and...