Size and condition of bamboo as structural factors behind the vertical stratification of the bamboo-nesting ant community

Abstract

Nest-site limitation is an important factor regulating ant diversity, particularly at low elevations. In savannas, trees and shrubs do not support large nests in their crowns and cavities for nest sites are limited. However, bamboos are very common and can provide vertically stacked hollow chambers for ants to establish their colonies. We evaluated the bamboo species Guadua paniculata as a source of nest cavities for ants in the Cerrado (Brazilian savanna). We hypothesized that the morphology of this bamboo species and its vertical arrangement regulate the distribution of ants nesting in it. Thirty bamboo patches distributed among four sites in the state of Tocantins (Brazil) were evaluated, in which 36 species of ants occupied more than half of the bamboo available. Wider and longer culms enabled a greater number of colonies of several ant species. Living or dead condition of bamboo had a significant effect on the diversity and composition of the ant fauna. Dead culms were occupied opportunistically by several generalist species, while Azteca fasciata dominated living bamboo. Finally, we observed the species distribution along a vertical gradient of bamboo height, and proposed that differential colonization of ground and canopy-dwelling species and habitat specialization may be key mechanisms for the observed pattern of distribution. This study contributes to a better understanding of species coexistence in low elevation forests in the Brazilian Cerrado by considering bamboo nest sites as a key factor affecting ant diversity.