Resource edibility and trophic exploitation in an old-field food web

I tested a food web model that predicts how environmental productivity (nutrient supply) and top carnivores should mediate interactions among herbivores, edible plants, and plants that are resistant to herbivory because they possess anti-herbivore defenses. Feeding trials with the dominant grasshopp...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1994-06, Vol.91 (12), p.5364-5367
Main Author: Schmitz, O.J
Format: Article
Language:English
Subjects:
Acrididae
Araneae
Biomass
Biomass production
CADENA ALIMENTARIA
CHAINE ALIMENTAIRE
COMPOSITAE
DEPREDADORES
ECOLOGIA ANIMAL
ECOLOGIE ANIMALE
Ecology
Edible plants
Flowers & plants
Food chains
Food webs
FRAGARIA
HERBIVORE
Herbivores
HERBIVOROS
Insecta
LYCOSIDAE
MELANOPLUS
NIVEAU TROPHIQUE
NIVELES TROFICOS
Nutrient nutrient interactions
ONTARIO
Orthoptera
PELOS VEGETALES
PHLEUM PRATENSE
Plants
POIL VEGETAL
PREDATEUR
Productivity
SOLIDAGO
Trichomes
Trophic relationships
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Summary:I tested a food web model that predicts how environmental productivity (nutrient supply) and top carnivores should mediate interactions among herbivores, edible plants, and plants that are resistant to herbivory because they possess anti-herbivore defenses. Feeding trials with the dominant grasshopper herbivore at the study site confirmed that certain plant species were resistant to herbivory because of protection by pubescent leaves and stems. Experimental food webs with various numbers of trophic levels composed of edible and resistant plants, grasshoppers, and hunting spiders were assembled in enclosure cages. I randomly assigned half of the cages to a nutrient-enrichment treatment and half remained as a control. Nutrient supply directly enhanced primary productivity and plant and herbivore biomass. Experimentally changing spider abundance caused a classic "trophic cascade" in which herbivore biomass increased and edible plant biomass decreased. Resistant plant biomass increased. These results matched predictions of the model with one exception. A trophic cascade was not observed under enriched conditions. The study nevertheless shows that a simple model attempting to explain heterogeneous interactions in food webs may give considerable insight into the dynamics of natural systems.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.91.12.5364