Recently, many studies have shown that prey organisms can change their behavior, physiology, and morphology in response to the presence of their predators. For example, presence of predators often reduces feeding activity and/or trigger habitat shift of herbivores, which, in turn, increases plant biomass. On the other hand, plants also change their traits in response to attack by herbivores. The magnitude of induced plant responses is largely dependent on patterns of herbivory, such as the amount of damage and position receiving damage. Hence, we hypothesize that predators can alter herbivore-induced plant responses through a behavioral shift of herbivores.

We conducted a field experiment to test the hypothesis, using a tri-trophic system of a willow, a leaf beetle larva, and a flower spider. The experiment had four treatments: lethal (tri-trophic with a spider) and risk (tri-trophic with a manipulated predator whose chelicerae were glued), no predator (bi-trophic), and control (plant alone) treatments.

We found significant predator effects on changes in willow leaf quality in response to damage by the leaf beetle. We discuss how the presence of spiders can make “trait change cascade”.