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 km2, 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.

The role of Senescent Stem-Galls over Arboreal Ant Communities Structure in Eremanthus erythropappus (DC.) MacLeish (Asteraceae) Trees

“…Other important resources provided by plants to ants are nesting sites and shelter, such as domatias or cavities produced by the activity of endophytic insects (Oliveira & Freitas, 2004;Schoereder et al, 2010;Nascimento et al, 2012;Almeida et al, 2014). Therefore, the supply of food resources and places for shelter and nesting are both determining factors for the establishment and survival of arboreal ants on trees (Oliveira & Freitas, 2004).…”

Senescent stem-galls in trees of Eremanthus erythropappus as a resource for arboreal ants

“…Furthermore, the presence of galleries and stem-galls within the twigs (created by borer and gall inducing insects) are an excellent advantage and help greatly in the construction of nests by arboreal ants (Fernandes et al 1988;Araújo et al 1995;Oliveira & Freitas 2004;Schoereder et al 2010). As in the cerrado, the high diversity of galls in other plant formations such as the Atlantic forest (Coelho et al 2013;Carneiro et al 2014) and dry forests (Coelho et al 2013) suggest that these galls can be widely used by ants in these environments.…”

Microhabitat Characteristics That Regulate Ant Richness Patterns: The Importance of Leaf Litter for Epigaeic Ants

“…Thus, each microhabitat characteristic may affect differently ants of distinct strata. For example, the diversity of arboreal ants can be closely linked to the presence, quality and quantity of resources from the trees, as extrafloral nectaries or presence of trophobiont insects and other nitrogen-rich resources (Yanoviak & Kaspari, 2000;Schoereder et al, 2010). Therefore, it is possible to infer that this stratum will be the first to suffer with changes in vegetation structure.…”