Rainforest Canopy Ants: The Implications of Territoriality and Predatory Behavior

Abstract

After first being ground-nesters and predators or scavengers, ants became arboreal with the rise of angiosperms and provided plants a biotic defense by foraging for prey on their foliage. Plants induce ants to patrol on their leaves through food rewards (e.g., extra-floral nectar and food bodies), while ants attend hemipterans for their honeydew. Most arboreal-nesting ants build their own nests, but myrmecophytes, plants that offer hollow structures that serve as nesting places to specialized “plant-ants”, illustrate the tight evolutionary bonds between ants and plants. In tree-crop plantations and in some rainforest canopies territorially-dominant arboreal ants have large colonies with large and/or polydomous nests. Their territories are defended both intra- and interspecifically, and are distributed in a mosaic pattern, creating what has become known as “arboreal ant mosaics”. They tolerate non-dominant species with smaller colonies on their territories. Arboreal ant mosaics are dynamic because ant nesting preferences differ depending on the species and the size and age of supporting trees. Because the canopy is discontinuous, arboreal-foraging ants can be found in ant mosaics; invasive ants can affect also the structure of the mosaic. We discuss here the methods that permit us to study these mosaics. Territorially-dominant arboreal ants are good predators that use group ambushing to catch flying insects on their host tree foliage. When producing winged sexuals they also forage for prey on the ground and plunder the colonies of non-dominant species sharing their host tree. When expanding their territories, the workers of the victorious colony raid the defeated colony. Because territorially-dominant arboreal ants prey on herbivores and strongly affect their general activity, ants are frequently used as biological control agents.