Functional identity of dominant species in a predator community prevails over functional diversity in shaping the top-down control of herbivores

Decline in species richness as well as changes in community evenness or functional diversity have been hypothesized to jointly affect ecosystem functioning. However, disentangling the relative effects of these changes in community structure is hard as these different aspects often covary with species richness in real-world ecosystems. In this study, we investigated the individual and interactive effects of functional diversity and community evenness of predators on the level of control of herbivorous prey. 
Using a highly-replicated mesocosm experiment, we crossed three levels of functional diversity of arthropod predators with two levels of community evenness while controlling for the effect of species richness. Using this experimental setting, we hypothesized that the effect size of functional diversity of predators depends on community evenness. We expected a positive effect of functional diversity of predators on top-down control at a high level of community evenness while we thoug..., To test how functional diversity modulates the effect of evenness in predator communities on herbivore consumption rates, we set up a mesocosm experiment that crossed three levels of functional diversity of predators with two levels of community evenness. We selected the aphid Acyrtosiphon pisum and the leafhopper Euscelidius variegatus as the two main herbivorous species for the experiment. Eleven predator species that are known to prey on aphids and leafhoppers and that are common predators found in grassland or faba bean fields were selected to define predator assemblages used in the experiment. In order to assemble three-species communities that represent three contrasted levels of functional richness, we first characterized these species using six functional traits involved in the predation. We collected information about body size (mm), circadian activity (diurnal, nocturnal), habitat domain (soil, foliage), hunting mode (ambush hunters, active hunters), averaged handling time (lo...,