Roads Alter the Colonization Dynamics of a Keystone Herbivore in Neotropical Savannas

Abstract

Roads can facilitate the establishment and spread of both native and exotic species. Nevertheless, the precise mechanisms facilitating this expansion are rarely known. We tested the hypothesis that dirt roads are favorable landing and nest initiation sites for founding-queens of the leaf-cutter ant Atta laevigata. For 2 yr, we compared the number of attempts to found new nests (colonization attempts) in dirt roads and the adjacent vegetation in a reserve of cerrado (tree-dominated savanna) in southeastern Brazil. The number of colonization attempts in roads was 5 to 10 times greater than in the adjacent vegetation. Experimental transplants indicate that founding-queens are more likely to establish a nest on bare soil than on soil covered with leaf-litter, but the amount of litter covering the ground did not fully explain the preference of queens for dirt roads. Queens that landed on roads were at higher risk of predation by beetles and ants than those that landed in the adjacent vegetation. Nevertheless, greater predation in roads was not sufficient to offset the greater number of colonization attempts in this habitat. As a consequence, significantly more new colonies were established in roads than in the adjacent vegetation. Our results suggest that disturbance caused by the opening of roads could result in an increased Atta abundance in protected areas of the Brazilian Cerrado.