Ant–plant–herbivore interactions in the neotropical cerrado savanna

Abstract

The Brazilian cerrado savanna covers nearly 2 million km2 and has a high incidence on foliage of various liquid food sources such as extrafloral nectar and insect exudates. These liquid rewards generate intense ant activity on cerrado foliage, making ant-plant-herbivore interactions especially prevalent in this biome. We present data on the distribution and abundance of extrafloral nectaries in the woody flora of cerrado communities and in the flora of other habitats worldwide, and stress the relevance of liquid food sources (including hemipteran honeydew) for the ant fauna. Consumption by ants of plant and insect exudates significantly affects the activity of the associated herbivores of cerrado plant species, with varying impacts on the reproductive output of the plants. Experiments with an ant-plant-butterfly system unequivocally demonstrate that the behavior of both immature and adult lepidopterans is closely related to the use of a risky host plant, where intensive visitation by ants can have a severe impact on caterpillar survival. We discuss recent evidence suggesting that the occurrence of liquid rewards on leaves plays a key role in mediating the foraging ecology of foliage-dwelling ants, and that facultative ant-plant mutualisms are important in structuring the community of canopy arthropods. Ant-mediated effects on cerrado herbivore communities can be revealed by experiments performed on wide spatial scales, including many environmental factors such as soil fertility and vegetation structure. We also present some research questions that could be rewarding to investigate in this major neotropical savanna.

Distribution, structural and ecological aspects of the unusual leaf nectaries of Calolisianthus species (Gentianaceae)

“…EFNs occur in 93 families of flowering plants, and such plants bearing EFNs account for 30% of the species in some environments (Rudgers and Gardener, 2004). Plants bearing EFNs are visited by nectarforaging insects, especially ants, wasps, bees, flies and beetles (Cuautle and Rico-Gray, 2003, Koptur, 1992and Oliveira and Freitas, 2004. Ants are the most common visitors to EFNs (do Nascimento and Del-Claro, 2010, Koptur, 1992 andOliveira, 1997), and numerous experimental field studies have shown a facultative ant-plant mutualism, where ants are attracted to the nectaries and in turn offer the plant varying degrees of anti-herbivore protection (Cuautle and Rico-Gray, 2003, Katayama and Suzuki, 2003.…”

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

“…In the environment of the Brazilian cerrado, the high concentration of arboreal ants can be explained by the diversity of food sources available within the vegetation, such as extrafloral nectar and insect honeydew (Oliveira & Freitas 2004). 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).…”

“…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.…”

Are stem nectaries common in Gentianaceae Juss.?

“…EFNs have been considered more abundant in species from tropical communities than in those from temperate regions (Oliveira & Freitas 2004;Rico-Gray & Oliveira 2007). However, information about the possible influences of geographic regions over the occurrence of EFNs is still scarce (Pemberton 1998).…”