Ant assemblages are almost all related with the vegetation composition and so can provide us important information for conservation strategies, which are especially relevant to an environmentally protected area. We sampled the ant fauna in three different phytophysionomies in order to verify if the composition of ant species is different among the areas, especially because one of the areas is a Rocky Field and there is little information about the ant fauna in this habitat. A total of 8730 individuals were registered and an NMDS analysis showed that the ant assemblies are different at the three phytophysionomies (Rocky Field, Riparian Forest, and Secondary Forest). This study shows that the species that compose the ant assemblies in different phytophysionomies are a reflex of the environment, supporting the hypothesis that the vegetational composition results in different compositions in the ant assembly. Vegetal composition is determinant in the formation of the litter and consequently in the occurrence of ant species that depend on this layer of organic matter for nesting and foraging.

Foraging networks are a key element for ant colonies because they facilitate the flow of resources from the environment to the nest and they allow the sharing of information among individuals. Here we report the results of an 8-month survey, extending from November 2009 to June 2010, of the foraging networks of four mature colonies of Atta bisphaerica, a species of grass-cutting ant which is considered as a pest in Brazil. We found that the distribution of foraging effort was strongly influenced by the landscape features around the nests, in particular by the permanently wet parts of the pasture in which the nests were located. The foraging networks consisted of underground tunnels which opened on average at 21.5m from the nests and of above-ground physical trails that reached on average 4.70m in length. The use of the foraging networks was highly dynamic, with few sections of the networks used for long periods of time. Three different phases, which could be linked to the seasonal change in the local rainfall regime, could be identified in the construction and use of the foraging networks. The first phase corresponded to the beginning of the rainy season and was characterized by a low foraging activity, as well as a low excavation and physical trail construction effort. The second phase, which began in February and extended up to the end of the humid season at the end of March, was characterized by an intense excavation and trail construction effort, resulting in an expansion of the foraging networks. Finally, in the third phase, which corresponded to the beginning of the dry season, the excavation and trail construction effort leveled off or decreased while foraging activity kept increasing. Our hypothesis is that ants could benefit from the underground tunnels and physical trails built during the humid season to maintain their foraging activity at a high level.

No abstract

Artrópodes, em especial os insetos, têm um papel interessante na vetoração de parasitos devido à sua ampla distribuição em diferentes habitats bem como seus hábitos alimentares. Thyssen et al. (2004)

Social information exchange through physical contacts and chemical trail deposition forms the basis of food recruitment in leaf-cutting ants. The scout initiates the process and passes the information to nestmates that recruit more foragers, thus amplifying the stimulus and ensuring the success of foraging. An interruption of the contact between workers and a reduction in trail laying can diminish the effectiveness of mass recruitment and alter scouting activity and forager flow. This study verified an increase in scout trips as a consequence of inbound workers (with or without a plant load) removal during Atta sexdens foraging, sustaining the outbound flow of foragers, and consequently foraging activity, either through direct contact or chemical trail deposition. Data indicate as one of the roles of unladen workers along the foraging trail must be to stimulate other workers to go out and so speed up the recruitment process The remarkable ability to organize themselves without central control is a major strength of social insects and the increase in scouting activity observed here is an example of this behavioral flexibility in leaf-cutting ants. Although foraging performance is enhanced through communication between workers, the simple adjustment in scouting activity can maintain the outbound flow of foragers which is an essential activity of the colony.