Insect and plant traits drive local and landscape effects on herbivory in grassland fragments

Péter Batáry,Martín Videla,Verena Rösch,Maria Rosa Rossetti,Teja Tscharntke

doi:10.1002/ecs2.2717

Abstract

AbstractHerbivory is one of the most important antagonistic insect–plant interactions and can be influenced by factors at local and landscape scales. Landscape fragmentation may reduce herbivory directly (i.e., decreasing abundance and species richness of herbivores), but also indirectly increase herbivory (i.e., releasing herbivores from top‐down control). At a local scale, reduced plant diversity may enhance herbivory through lessened associated resistance, while resource availability (i.e., higher vegetation height and cover) may promote herbivory. Few studies have simultaneously considered the influence of local and landscape variables on insect herbivory. We evaluate effects of landscape (fragment size, connectivity, and arable land percentage) and local factors (plant cover and height and plant species richness) on insect herbivory in fragmented calcareous grasslands. Further, we ask whether these effects depend on feeding traits of herbivores (chewers vs. suckers) and habitat specialization of plants (specialists vs. generalists). Results show that herbivory was best explained by models including variables at both local and landscape scales. However, local factors were more important than landscape variables. Herbivory was in all cases positively related to height of herbs (i.e., taller and more heterogeneous food resources), whereas the effect of plant species richness varied with feeding traits of herbivores. Herbivory by chewers, which are commonly more generalist feeders, was negatively affected by plant species richness, supporting the idea of associated plant resistance. In contrast, herbivory by suckers, which tend to be more specialized, increased with plant richness. Although there was little influence of landscape scale, herbivory on specialist plants was significantly higher in smaller grasslands probably as a consequence of herbivore release from natural enemies. Functional redundancy among herbivore species would allow to maintain overall herbivory in fragmented calcareous grasslands. This study highlights the need to consider different herbivore and plant traits for a better understanding of herbivory responses to local and landscape factors.

Highlights

Insect herbivory is one of the most important antagonistic interactions between plants and animals, since it affects plant performance and thereby vegetation structure and plant community composition (Crawley 1989)
The same pattern would be expected for insect herbivory in landscapes dominated by arable land, this needs to be examined since most of the studies so far have focused on other ecosystem processes like predation and parasitism (Chaplin-Kramer et al 2011)
We aimed to answer the following questions: (1) How is insect herbivory influenced by habitat fragmentation and local variables? (2) Do the landscape and local effects depend on insect and/or plant traits? We expect a higher influence of landscape variables on leaf damage on specialist plants and on sucking herbivory since the most abundant species of suckers have narrower diet breadths than the most abundant species of chewers in these calcareous grasslands (Kormann et al 2015)

Summary

Introduction

Insect herbivory is one of the most important antagonistic interactions between plants and animals, since it affects plant performance and thereby vegetation structure and plant community composition (Crawley 1989). Habitat fragmentation can influence insect herbivory via direct negative effects on species richness and abundance of herbivores (Wirth et al 2008). Lower abundance and species richness of herbivores in smaller fragments can lead to decreased herbivory (e.g., Faveri et al 2008, Nufio et al 2011). These species and herbivory declines can be exacerbated by fragment isolation that usually increases in fragmented landscapes and hamper herbivore movement among habitats (Ro€sch et al 2013, Brudvig et al 2015, Maguire et al 2015). The same pattern would be expected for insect herbivory in landscapes dominated by arable land, this needs to be examined since most of the studies so far have focused on other ecosystem processes like predation and parasitism (Chaplin-Kramer et al 2011)

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Conclusion