Impact of tree isolation on arboreal and ground ant communities in clearedpasture in the Atlantic rain forest region of Bahia, Brazil

The Atlantic rain forest of south-eastern Brazil has been substantially cle ared, resulting in the creation of a fragmented landscape. In addition to t he small fragments of forest that remain, the pasture is often scattered wi th isolated trees. This paper investigates the capacity of these isolated t rees to support representatives of the original Atlantic rain forest ant co mmunities and also how these arboreal ants interact with the disturbance-as sociated ant fauna of the pasture beneath them. Twenty trees in the grassla nd, representing a range of distances from the forest, and 10 trees within the forest, were selected for sampling. Arboreal ants were sampled by hand collection and chemical knockdown, while the ants on the ground beneath wer e sampled by pitfall traps and Winkler sacks. Pasture trees supported a mod erately high richness of arboreal ant species. The richness of ants on past ure trees appears to be independent of distance from forest, although this might become a significant factor on trees that are more isolated than thos e studied here. Ant species richness on pasture trees is higher if the tree s are large, support a high epiphyte load and are native to the area. Isola ted trees within the agricultural matrix therefore play some role in conser ving elements of the original forest ant fauna. Since some of the species o n pasture trees have been observed to reach dominant or sub-dominant status in nearby forest and cocoa farms, they may play some role in limiting pest outbreaks in the pasture close to the trees. If this is so, there may be a case for retaining an adequate density of trees to enable the influence of arboreal ants to extend over as much pasture as possible.