Ant-plant dynamics: the effects of leaves and scale insects on ant species richness and abundance on Acacia grandicornuta and Acacia robusta

In this study, we examined whether leaf presence affected ant abundances on Acacia grandicornuta, and how the presence of scale insects on Acacia robusta affected ant species abundance. In order to asses the benefits accrued by the plants, we also tested attack times of three genera of ants following a disturbance to the host tree. It was determined that both ant species richness and concentration were significantly greater on A. grandicornuta containing leaves. This result suggests that the presence of leaves drives the mutualism between A. grandicornuta and ants, and when leaves are not present, ant concentrations decrease. We also determined that Black Sugar Ants (Lepisiota capensis) exist in greater abundance on A. robusta when scale insects are present, and this populace of L. capensis correlates to a reduction in the abundance of other ant species. Finally, our results show that L. capensis attack significantly quicker than other ant genera following a disturbance to the host tree. This demonstrates the ability of L. capensis to colonize and dominate a host tree, causing a significant decrease in the abundance of other ant genera. These results convey that a facultative mutualism exists among A. robusta, L. capensis, and scale insects; L. capensis provides protection for both A. robusta and scale insects, while scale insects offer nutritional benefits to the resident ants.