Antagonistic Interactions in the Rupestrian Grasslands: New Insights and Perspectives

Abstract

Antagonistic interactions are main ecological forces in terrestrial communities and include several examples involving plants and animals. The studies performed in the rupestrian grasslands have mostly focused on patterns of herbivory and on the effects of plant quality and natural enemies on insect herbivore abundance and distribution. Herbivory rates recorded for plants in this ecosystem are within the range proposed for open areas (ca. 15 %), although a wider range of studies are still needed. Galling insect richness is highly variable amongst sites (between 18 and 241 species) and are mostly rich and abundant in xeric habitats compared to mesic habitats, corroborating the hypothesis of environmental harshness. Several new galling insect species have been discovered in this very diverse landscape, indicating its importance for insect radiation and evolution. Galling insect communities associated to host plants are influenced by host plant sex. Male plants generally host higher insect richness and herbivory levels than female plants. Gall insect richness sampled on 138 host plants in several rupestrian grassland sites indicates that larger plant families also host higher number of galling insects than smaller plant families or genera. Amongst the factors that influence host plant selection by herbivores in rupestrian grasslands aspects of plant quality such as leaf asymmetry, leaf sclerophylly and ant-interactions have been evaluated. However, mixed results for the effects of plant quality on insect abundance and performance have been found depending upon the insect-host system evaluated. Another antagonist interaction evaluated involves parasitism by two common species of mistletoes and results have shown that parasitism represents another important source of stress for host plants in the rupestrian grasslands. Finally, in this chapter we summarize several antagonistic, multitrophic and indirect interactions using plants in the genus Baccharis as a model, aiming to provide information and guidance for future studies.