Structure of mutualistic ant-treehopper interactions in the Brazilian Atlantic Forest

Ant-treehopper mutualisms are centred on the availability of honeydew, a sugary fluid offered by treehoppers to attract ants, which respond by defending their hosts against predators and parasitoids. However, due to differences in the treehopper social behaviour (i.e. the amount of food resource available) ants can monopolize treehopper aggregations in many ways. Here we evaluated the topological structure of quantitative ant-treehopper interaction networks in three Brazilian Atlantic Forest localities. Moreover, we specifically investigated the role of ant recruitment strategy and treehopper behaviour in the structure of these networks. For this, we sampled ant-treehopper interactions along representative transects (6 km per site) within each studied site and recorded the mean number of individuals of treehopper and ant species. We found that independent of variation in environmental factors among study sites, ant-treehopper networks were highly compartmentalized (Mean +/- SD: Q = 0.34 +/- 0.1) when compared with null models, and exhibit low connectance (C = 0.18 +/- 0.01) and specialization (H-2' = 0.36 +/- 0.08) values. In addition, we also observed that larger aggregations of treehoppers interacted with a higher number of ant species and ants that were locally dominant and showed massive recruitment interacted with a larger number of treehopper species. In summary, our results illustrate the importance of foraging strategies in shaping ecological interactions in tropical environments.