Ant Species Identity has a Greater Effect than Fire on the Outcome of an Ant Protection System in Brazilian Cerrado

Although fire- and ant-plant interactions influence the community structure and dynamics of Neotropical savannas, no previous studies have considered their simultaneous effects on target host plants. We monitored the effect of ant exclusion for 3years on leaf area loss to leaf chewing insects, thrips abundance, and reproductive output of the extrafloral nectary-bearing shrub, Peixotoa tomentosa (Malpighiaceae). We predicted that the impact of ants on herbivores and plants would depend on the ant species, and that fire would reduce the effect of ants. We deliberately chose control plants that differed in their occupant ant species. Fire occurred in the second year of the study, allowing us to determine its effect on the benefit afforded by ants. Ants reduced leaf area loss and thrips abundance, and increased fruit and seed production in all 3years. Some ant species were more effective than others, while plants with multiple ant species suffered higher leaf area loss than plants with a single ant species. In the year following the fire, leaf damage was greater than in the other years, regardless of the ant species, and the proportional effect of ants in reducing damage was less. Interactions affecting thrips abundance did not change following fire, nor was the benefit to the plant proportionally reduced. Overall, the identity of the ant species had a greater effect than did the occurrence of fire on the ant-herbivore-plant interaction: the identity of the ant species influenced leaf area loss, thrips numbers, and bud and seed production, while fire only modified the impact of ants on the amount of leaf area consumed by insect herbivores.