Induced defenses in herbivores and plants differentially modulate a trophic cascade

• Published in: Ecology (Durham) Vol. 88; no. 10; pp. 2474 - 2481
• Main Authors: Stap, I. van der, Vos, M, Verschoor, A.M, Helmsing, N.R, Mooij, W.M
• Format: Journal Article
• Language: English
• Published: Washington, DC Ecological Society of America 01-10-2007
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Asplanchna; Biological and medical sciences; Biomass; bottom-up control; Brachionus calyciflorus; Brachionus rubens; Carnivores; defense mechanisms; Desmodesmus bicellularis; Ecology; Ecosystem; Eukaryota - growth & development; Feeding Behavior; Flowers & plants; Food Chain; Food chains; Food webs; Fundamental and applied biological sciences. Psychology; General aspects; Herbivores; inducible defenses; interaction strength; Marine ecology; Models, Biological; phenotype; phenotypic plasticity; Plankton - growth & development; Plant ecology; Population Dynamics; predator-prey relationships; Predators; Predatory Behavior - physiology; predator–prey interactions; resistance mechanisms; Rotifera; Scenedesmaceae; Scenedesmus obliquus; top-down control; trait-mediated interactions; traits; Trophic cascades; trophic relationships; zooplankton; Predator prey relation; Herbivorous; Interaction; Phenotypic plasticity; inducible defenses; Bottom up control; Plant; Induced defense; Top down control; interaction strength; top-down control; Trophic cascade; trait-mediated interactions; predator- prey interactions; bottom-up cotitrol
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/07-1731.1

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.