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Terrestrial deposition of aquatic insects increases plant quality for insect herbivores and herbivore density

Authors

  • HILARY BULTMAN,

    Corresponding author
    1. Department of Entomology, University of Wisconsin, Madison, Wisconsin, U.S.A.
    2. Department of Zoology, University of Wisconsin, Madison, Wisconsin, U.S.A.
    • Correspondence: Hilary Bultman, 1630 Linden Drive, Madison, WI 53706-1598, U.S.A. E-mail: hlbultman@wisc.edu

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  • DAVID HOEKMAN,

    1. Department of Entomology, University of Wisconsin, Madison, Wisconsin, U.S.A.
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    • Current address: Department of Insect Ecology, National Ecological Observatory Network, 1685 38th Street, Ste. 100, Boulder, CO 80301, U.S.A
  • JAMIN DREYER,

    1. Department of Entomology, University of Wisconsin, Madison, Wisconsin, U.S.A.
    2. Department of Zoology, University of Wisconsin, Madison, Wisconsin, U.S.A.
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  • CLAUDIO GRATTON

    1. Department of Entomology, University of Wisconsin, Madison, Wisconsin, U.S.A.
    2. Department of Zoology, University of Wisconsin, Madison, Wisconsin, U.S.A.
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Abstract

1. Mobile organisms such as emergent aquatic insects can subsidise land with aquatic nutrients, creating a link between terrestrial and aquatic ecosystems.

2. Deposition of aquatic insects on land produces bottom-up effects in arthropod detritivore communities and may also affect plants and plant–herbivore interactions.

3. To investigate the effects of insect deposition on plant–herbivore interactions, we conducted a field experiment and surveys of tealeaf willow (Salicaceae; Salix phylicifolia Coste) and July highflyer caterpillars (Geometridae; Hydriomena furcata Thunberg) at lakes in Northeast Iceland with either high- or low-midge density and deposition to land.

4. It was found that willow at high-midge lakes had 8–11% higher nitrogen content compared with willow at low-midge lakes. In addition, natural caterpillar density was 4–6 times higher and caterpillars were 72% heavier at high-midge lakes than low-midge lakes.

5. A fully reciprocal caterpillar transplant experiment among willow at high- and low-midge lakes was performed to separate the influence of habitat and midge effects on caterpillar performance.

6. After transplant, pupae of July Highflyer caterpillars were on average 11% heavier at high-midge sites compared with low-midge sites. However, this difference was not statistically significant.

7. The present findings indicate that cross-ecosystem subsidies in the form of aquatic insects can increase plant foliar quality and the abundance of insect herbivores in recipient ecosystems.

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