The arboreal ant Azteca sericeasur is a keystone ant species in shaded coffee farms, where it nests in canopy trees. It can have a mutualistic relationship with the scale insect Coccus viridis and has been shown to reduce pest burden on nearby coffee bushes.
Our research examined the effect of A. sericeasur on the decomposition of leaf litter of the predominant shade tree, Inga micheliana. We hypothesize that by excluding other ants A. sericeasur might affect leaf litter decomposition through two indirect mechanisms: 1) the soil surrounding A. sericeasur nests may be more compacted and have slower infiltration; and 2) important decomposers, like springtails, may be released from predation pressure. Determining the relative strengths of these interactions can illuminate the importance of A. sericeasur in decomposition and nutrient cycling processes.
Ten shade trees with A. sericeasur nests were paired with shade trees of the same species, without nests. Tuna baits were used to assess the ant community in 5 meter transects from each shade tree. To assess the soil organisms and provide additional assessment of the ant community, four pitfall traps were placed at each tree, at 0.5 and 2 meters from the tree in two cardinal directions. Infiltration was assessed at 6 sites, with increasing distance from the tree. Litterbags with I. micheliana leaf litter were 1 m from each tree for one year with collections at 2 weeks and 1, 2, 4, 6, 8, 10 and 12 months. Mass loss was used as a proxy for decomposition.
Results/Conclusions
A. sericeasur excluded ground-nesting ant species within the immediate radius of their nesting shade tree, but there was no significant difference in ant community composition beyond one meter from the nesting tree. There was no correlation between the infiltration rate or soil compaction and the presence of A. sericeasur or the abundance of total ants. Furthermore, the decomposer communities, as assessed via pitfall traps, were the same between trees with and without A. sericeasur and at 0.5 and 2 meters from the tree. There was faster leaf litter decomposition at sites without A. sericeasur, in comparison to sites with A. sericeasur. Our data is unable to fully explain this trend, but it is possible that presence of A. sericeasur is indirectly decelerating decomposition processes through physical and community mechanisms.