title: Abiotic mediation of a mutualism drives herbivore abundance.
abstract: Species abundance is typically determined by the abiotic environment, but the extent to which such effects occur through the mediation of biotic interactions, including mutualisms, is unknown. We explored how light environment (open meadow vs. shaded understory) mediates the abundance and ant tending of the aphid Aphis helianthi feeding on the herb Ligusticum porteri. Yearly surveys consistently found aphids to be more than 17-fold more abundant on open meadow plants than on shaded understory plants. Manipulations demonstrated that this abundance pattern was not due to the direct effects of light environment on aphid performance, or indirectly through host plant quality or the effects of predators. Instead, open meadows had higher ant abundance and per capita rates of aphid tending and, accordingly, ants increased aphid population growth in meadow but not understory environments. The abiotic environment thus drives the abundance of this herbivore exclusively through the mediation of a protection mutualism.
authors.affiliation: Department of Biology, University of Colorado at Colorado Springs, 1420 Austin Bluffs Parkway, Colorado Springs, CO, USA.|Rocky Mountain Biological Laboratory, PO Box 319, Crested Butte, CO, 81224.
authors.forename: Emily H
authors.initials: EH
authors.lastname: Mooney
authors.affiliation: Rocky Mountain Biological Laboratory, PO Box 319, Crested Butte, CO, 81224.|University of Nebraska-Lincoln, 1400 R St, Lincoln, NE, 68588.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Phillips
authors.affiliation: Linfield College, 900 SE Baker St, McMinnville, OR 97128.
authors.forename: Chadwick V
authors.initials: CV
authors.lastname: Tillberg
authors.affiliation: Rocky Mountain Biological Laboratory, PO Box 319, Crested Butte, CO, 81224.|State University of New York at Oswego, 7060 NY-104, Oswego, NY, 13126.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Sandrow
authors.affiliation: Rocky Mountain Biological Laboratory, PO Box 319, Crested Butte, CO, 81224.|University of California at Irvine, 321 Steinhaus Hall, Irvine, CA, 92697.
authors.forename: Annika S
authors.initials: AS
authors.lastname: Nelson
authors.affiliation: Rocky Mountain Biological Laboratory, PO Box 319, Crested Butte, CO, 81224.|University of California at Irvine, 321 Steinhaus Hall, Irvine, CA, 92697.
authors.forename: Kailen A
authors.initials: KA
authors.lastname: Mooney
mesh_terms: D000818:Animals; D001000:Ants / Q000502:physiology*; D001042:Aphids / Q000502:physiology*; D003120:Colorado; D060434:Herbivory; D030004:Ligusticum; D011156:Population Density; D011235:Predatory Behavior; D013472:Sunlight; D013559:Symbiosis
keywords: Ant-aphid mutualism; Ligusticum porteri; light environment; multi-trophic interactions