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

Abstract

The extensive occupation of canopy trees by ants can be attributed to many factors, such as the presence of structures that provide food and shelter. Structures induced by other insects in host plants, like senescent galls, can provide shelter and a nesting place for many species of ants. The main objectives of this work were: (1) to describe the ant communities found in canopies of candeia trees (Eremanthus erythropappus), including the species which use galls as nesting sites; (2) verify the role of galls in determining the structure and composition of the ant communities and (3) to evaluate whether the size and shape of galls are important to the choice of nesting sites by ants. Specifically, the following questions were investigated: 1 – Are larger galls more frequently occupied by ants than smaller galls? 2 – Does gall shape (globular and fusiform) influence occupation? 3 – Which species of ants are present in the canopies of candeias and which are occupying galls? Senescent galls were collected in locations in the southern portion of the Espinhaço Mountain Range, state of Minas Gerais, southeastern Brazil. In total, 3,195 galls were collected and 19 ant species were recorded. Only 176 galls (5.5%) had been occupied by ants, and these were represented by 11 species. The most frequent species found occupying galls were Myrmelachista nodigera, with 48 colonies; Nesomyrmex spininodis, with 37 colonies; and Crematogaster complex crinosa sp. 1, with 29 colonies. The ants occupied galls with greater volume and diameter. Even considering the low occupation frequency, senescent galls in E. erythropappus are used by ants, either as outstations or satellite nests of polydomic colonies, and may be important in determining ant species composition in canopy trees.