The effect of experimental warming on insect herbivory in an alpine plant community

Abstract

Climate warming is predicted to affect species and trophic interactions worldwide, and alpine ecosystems are expected to be especially sensitive to changes. There are few studies on how insect herbivory respond to warming. Therefore, the aim of this study was to examine if experimental warming had an effect on herbivory by leaf-chewing insects in an alpine plant community. To manipulate the climate I used open-top chambers (OTCs) from an ongoing long-term experiment at Finse, Norway. By recording feeding damages on the vascular plants in the OTCs and in control plots, I found that warming increased the herbivory pressure on Dryas octopetala, but not on Bistorta vivipara and Salix reticulata. The increase was significant both in early and late season. Species-specific responses suggest that warming might have caused changes in herbivore activity or plant quality. A feeding preference experiment with the larvae of the moth Zygaena exulans, a common herbivore at the study site, showed a strong dislike for Saussurea alpina. However, no significant difference between the preference for D. octopetala, B. vivipara, S. reticulata, and S. herbacea was found. There was little consistence between the feeding experiment and the field registrations. This discrepancy might be caused by the presence of additional insect herbivore species in the field or the fact that the feeding experiment was based on an introductory no-choice test. Even with the limitations in using OTCs for herbivory research, the present study indicates that some species, such as D. octopetala, will be more susceptible to insect herbivory than others when temperatures increase. Although the impact of increased herbivory on plant performance has not been assessed in this study, the increase in damages on D. octopetala suggests that it is important to take insect herbivory into consideration when predicting changes in alpine plant communities due to climate warming.