The arboreal ant community visiting extrafloral nectaries in the Neotropical cerrado savanna

Abstract

The cerrado savanna of Brazil embraces an area of approximately 2 million km 2 , in which vegetation physiognomies may vary from open grassland to forest with a discontinuous herbaceous layer. Here we describe the main ecological factors accounting for the prevalence of ants on cerrado foliage, and present a general characterization of the arboreal ant fauna of this savanna. The high incidence of ants on cerrado foliage results mostly from the wide occurrence of predictable liquid food sources in the form of extrafloral nectaries (EFNs) and insect honeydew, which act as efficient promoters of ant activity on vegetation. In addition, stem galleries and cavities constructed by boring beetles and insect galls create a nesting space frequently used by arboreal ants. Specific studies involving ants, herbivores and plants are reported to demonstrate the impact that foliage-dwelling ants can have on phytophagous insects, herbivory levels, and ultimately on host plants. These studies show that: (i) ants visit EFNs and likely benefit from this resource; (ii) EFN-gathering ants can benefit particular plant species by reducing herbivory and increasing plant fitness; (iii) presence of EFNs does not affect ant species richness within a given tree; (iv) there is not a particular ant species composition typical of plants with EFNs; (v) although plants with EFNs are visited by more ant individuals than non-nectariferous plants, this visitation pattern does not translate into lower numbers of herbivores on the nectariferous plant community. We suggest some promising research avenues to elucidate how community-level parameters can be tied to the ecology of ant-plant associations in cerrado.