title: A chemical polymorphism in a multitrophic setting: thyme monoterpene composition and food web structure.
abstract: We investigated the effects of chemical variation in thyme (Thymus vulgaris L.) on its interactions with competitors, herbivores, and herbivore predators. Four different thyme monoterpene phenotypes (chemotypes) were grown in a 4x2x2 factorial of chemotype, caging (sham half-cages vs. full cages), and competition (control vs. the grass Bromus madritensis L.). Cages reduced numbers of arthropod predators. Thyme-feeding aphids Aphis serpylli Koch passed through full cage walls to increase more than fourfold. As a result, freed from their predators, aphids had a large negative effect on thyme size and flowering. Similarly, competition from Bromus had a negative effect on thyme size and flowering. Individual effects of aphids and competition were nonadditive, however, and their combined effect was significantly less than that predicted by a multiplicative null model. Differential thyme sizes among chemotypes were not mediated by herbivores or competitors, but differential flowering was due to the effects of chemotype on aphids. We thus document differential selection by aphids among thyme chemotypes and the influence of Bromus on the strength of these negative effects of aphids.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309, USA. yan.linhart@colorado.edu
authors.forename: Yan B
authors.initials: YB
authors.lastname: Linhart
authors.forename: Ken
authors.initials: K
authors.lastname: Keefover-Ring
authors.forename: Kailen A
authors.initials: KA
authors.lastname: Mooney
authors.forename: Bianca
authors.initials: B
authors.lastname: Breland
authors.forename: John D
authors.initials: JD
authors.lastname: Thompson
mesh_terms: D000821:Animal Feed; D000818:Animals; D001042:Aphids / Q000502:physiology*; D005502:Food; D005523:Food Supply; D014644:Genetic Variation; D019083:Mediterranean Region; D039821:Monoterpenes / Q000032:analysis*; D018521:Plant Physiological Phenomena; D006109:Poaceae / Q000502:physiology; D011110:Polymorphism, Genetic; D012903:Smell; D013649:Taste; D046930:Thymus Plant / Q000737:chemistry* / Q000235:genetics* / Q000469:parasitology
chemical_list: D039821:Monoterpenes