Advertisement

Experimental support of the stress-gradient hypothesis in herbivore–herbivore interactions

Authors

  • Olivier Dangles,

    Corresponding author
    1. Université Paris-Sud 11, Orsay Cedex, France
    2. Facultad de Ciencias Exactas y Naturales, Pontificia Universidad Católica del Ecuador, Quito, Ecuador
    • UR 072, LEGS-CNRS, CNRS, Institut de Recherche pour le Développement (IRD), Gif-sur-Yvette Cedex, France
    Search for more papers by this author
  • Mario Herrera,

    1. Facultad de Ciencias Exactas y Naturales, Pontificia Universidad Católica del Ecuador, Quito, Ecuador
    Search for more papers by this author
  • Fabien Anthelme

    1. UMR AMAP, CIRAD, Institut de Recherche pour le Développement (IRD), Montpellier Cedex, France
    Search for more papers by this author

Author for correspondence:

Olivier Dangles

Tel: +591 788 429 68

Email: olivier.dangles@ird.fr

Summary

  • The stress-gradient hypothesis (SGH) postulates an increase in the frequency of positive species interactions at increasing amounts of stress. While the SGH has been extensively tested in plant–plant interactions along abiotic stresses, it remains unclear whether this hypothesis could apply to higher trophic levels, such as herbivores, along biotic stress gradients.
  • To address this issue, we investigated how the interaction between two potato herbivores may change along a stress gradient created by an assortment of potato varieties with different tuber palatability. We used a tuber resistance trait as a measure for biotic stress and one herbivore as the facilitator to gain access to the tuber of the other herbivore.
  • Our experiment revealed a switch from neutral to positive interactions with increasing stress, confirming for the first time the predictions of the SGH for herbivores. Moreover, the intensity of facilitation decreased at high stress levels, suggesting that benefits by the facilitating species were dampened in the most stressful environment.
  • In view of the ubiquitous role played by positive interactions among herbivores, broadening our search image for facilitative effects among other plant enemies will allow a better awareness of the importance of the SGH in structuring plant communities.

Ancillary