How plants shape the ant community in the Amazonian rainforest canopy: thekey role of extrafloral nectaries and homopteran honeydew

Ant-plant interactions in the canopy of a lowland Amazonian rainforest of t he upper Orinoco, Venezuela, were studied using a modified commercial crane on rails (Surumoni project). Our observations show a strong correlation be tween plant sap exudates and both abundance of ants and co-occurrence of an t species in tree canopies, Two types of plant sap sources were compared: e xtrafloral nectaries (EFNs) and honeydew secretions by homopterans, EFNs we re a frequent food source for ants on epiphytes (Philodendron spp., Araceae ) and lianas (Dioclea, Fabaceae), but rare on canopy trees in the study are a, whereas the majority of trees were host to aggregations of homopterans t ended by honeydew-seeking ants ton 62% of the trees examined). These aggreg ations rarely occurred on epiphytes. Baited ant traps were installed on pla nts with EFNs and in the crowns of trees from three common genera, includin g trees with and without ant-tended homopterans: Goupia glabra (Celastracea e), Vochysia spp. (Vochysiaceae), and Xylopia spp. (Annonaceae). The number of ant workers per trap was significantly higher on plants offering one of the two plant sap sources than on trees without such resources. Extraflora l nectaries were used by a much broader spectrum of ant species and genera than honeydew, and co-occurrence of ant species tin traps) was significantl y higher on plants bearing EFNs than on trees. Homopteran honeydew (Coccida e and Membracidae), on the other hand, was mostly monopolised by a single a nt colony per tree. Homopteran-tending ants were generally among the most d ominant ants in the canopy. The most prominent genera were Azteca, Dolichod erus (both Dolichoderinae), Cephalotes, Pheiciole, Crematogaster (ali Myrmi cinae), and Ectatomma (Ponerinae). Potential preferences were recorded betw een ant and homopteran species, and also between ant-homopteran association s and tree genera. We hypothesize that the high availability of homopteran honeydew provides a key resource for ant mosaics, where dominant ant coloni es and species maintain mutually exclusive territories on trees. In turn, w e propose that for nourishment of numerous ants of lower competitive capaci ty, Philodendron and other sources of EFNs might be particularly important.