title: Variability in plant nutrients reduces insect herbivore performance.
abstract: The performance and population dynamics of insect herbivores depend on the nutritive and defensive traits of their host plants. The literature on plant-herbivore interactions focuses on plant trait mean values, but recent studies showing the importance of plant genetic diversity for herbivores suggest that plant trait variance may be equally important. The consequences of plant trait variance for herbivore performance, however, have been largely overlooked. Here we report an extensive assessment of the effects of within-population plant trait variance on herbivore performance using 457 performance datasets from 53 species of insect herbivores. We show that variance in plant nutritive traits substantially reduces mean herbivore performance via non-linear averaging of performance relationships that were overwhelmingly concave down. By contrast, relationships between herbivore performance and plant defence levels were typically linear, with variance in plant defence not affecting herbivore performance via non-linear averaging. Our results demonstrate that plants contribute to the suppression of herbivore populations through variable nutrient levels, not just by having low average quality as is typically thought. We propose that this phenomenon could play a key role in the suppression of herbivore populations in natural systems, and that increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems.
authors.affiliation: Department of Entomology and Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA.|Center for Population Biology, University of California, Davis, Davis, California 95616, USA.
authors.forename: William C
authors.initials: WC
authors.lastname: Wetzel
authors.affiliation: Center for Population Biology, University of California, Davis, Davis, California 95616, USA.|Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Kharouba
authors.affiliation: Center for Population Biology, University of California, Davis, Davis, California 95616, USA.
authors.forename: Moria
authors.initials: M
authors.lastname: Robinson
authors.affiliation: Department of Environmental Science and Policy, University of California, Davis, Davis, California 95616, USA.
authors.forename: Marcel
authors.initials: M
authors.lastname: Holyoak
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, Davis, California 95616, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Karban
mesh_terms: D000818:Animals; D020387:Food Chain; D060434:Herbivory; D007313:Insecta / Q000254:growth & development / Q000502:physiology*; D010944:Plants / Q000378:metabolism*; D011157:Population Dynamics