Herbivory mediated by coupling between biomechanical traits of plants and grasshoppers

1. Despite their potential to provide a mechanistic understanding of ecosystem processes, the functional traits that govern interaction networks remain poorly understood. We investigated the extent to which biomechanical traits are related to consumption in a plant—grasshopper herbivory network. 2. Using a choice experiment, we assessed the feeding patterns of 26 grasshopper species for 24 common plant species from subalpine grasslands. We quantified shear and punch toughness for each plant species, while grasshopper incisive and molar strengths were estimated by a lever mechanics model, following the measurement of mandibular traits. 3. Models incorporating co-phylogenetic effects showed that the ratio between the grasshopper incisive strength and plant toughness, that reflects the cutting effort, is correlated with the mass of plant eaten. Moreover, a strong relationship between the incisive strength of the grasshoppers and the weighed mean toughness of the plants they eat was found. 4. Our results suggest that biomechanical constraints imposed by plants influence the evolution of grasshoppers' mandibular traits. Such scaling relationships offer promising avenues towards the understanding of trait — function links in interaction networks.