title: Induced defenses in herbivores and plants differentially modulate a trophic cascade.
abstract: Inducible defenses are dynamic traits that modulate the strength of both plant-herbivore and herbivore-carnivore interactions. Surprisingly few studies have considered the relative contributions of induced plant and herbivore defenses to the overall balance of bottom-up and top-down control. Here we compare trophic cascade strengths using replicated two-level and three-level plankton communities in which we systematically varied the presence or absence of induced defenses at the plant and/or herbivore levels. Our results show that a trophic cascade, i.e., significantly higher plant biomass in three-level than in two-level food chains, occurred whenever herbivores were undefended against carnivores. Trophic cascades did not occur when herbivores exhibited an induced defense. This pattern was obtained irrespective of the presence or absence of induced defenses at the plant level. We thus found that herbivore defenses, not plant defenses, had an overriding effect on cascade strength. We discuss these results in relation to variation in cascade strengths in natural communities.
authors.affiliation: Netherlands Institute of Ecology (NIOO-KNA W), Centre for Limnology, Department of Food Web Studies, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands. i.vanderstap@nioo.knaw.nl
authors.forename: Irene
authors.initials: I
authors.lastname: Van der Stap
authors.forename: Matthijs
authors.initials: M
authors.lastname: Vos
authors.forename: Antonie M
authors.initials: AM
authors.lastname: Verschoor
authors.forename: Nico R
authors.initials: NR
authors.lastname: Helmsing
authors.forename: Wolf M
authors.initials: WM
authors.lastname: Mooij
mesh_terms: D000818:Animals; D018533:Biomass; D017753:Ecosystem; D056890:Eukaryota / Q000254:growth & development*; D005247:Feeding Behavior; D020387:Food Chain; D008954:Models, Biological; D010933:Plankton / Q000254:growth & development*; D011157:Population Dynamics; D011235:Predatory Behavior / Q000502:physiology*