Extrafloral nectar as a driver of arboreal ant communities at the site-scale in Brazilian savanna

Despite years of study, it remains unclear if and to what extent the effects of extra-floral nectaries (EFNs) on arboreal ants observed on individual trees scale up to larger spatial scales. Here, we address this issue in Brazilian savanna and tested three predictions: (i) Trees with EFN have higher richness of arboreal ant species than trees without; (ii) Arboreal ant species richness increases with the proportion of total EFN-bearing trees at the site scale, due to a higher occurrence of non-core ant species; (iii) Ant species composition changes with the proportion of EFN-bearing trees at the site scale. We sampled arboreal ants in 32 plots with EFN-bearing trees ranging from 0% to 60% of all trees. We sampled 72 ant species, from which 17 (mostly belonging to Camponotus, Cephalotes and Crematogaster) were identified as core species in at least one of the ant-EFN networks in the 32 plots. Ant species richness was significantly higher on EFN-bearing trees. We identified 11 ant species that preferentially occurred on EFN-bearing trees, all of which were core partners in networks. Species richness at the site scales increased with the proportion of EFN-bearing trees, regardless of tree density and richness; this pattern was due to a higher occurrence of non-core ant species. Finally, species composition also varied with the proportion of EFN-bearing trees. Therefore, we found that the presence of EFNs not only influences arboreal ants on individual trees but also has a substantial effect on the ant-EFN network on a broader community scale. The increase in non-core species site scale reveals that this interaction is unlikely to result in substantially enhanced protection services for EFN-bearing plants.