A New Case of Ants Nesting within Branches of a Fig Tree: the Case of Ficus subpisocarpa in Taiwan

Ficus is one of many plant genera involved in interactions with ants. The interaction is however little documented. We show here that ants, belonging mainly to the genus Crematogaster, nest in hollow internodes of young branches of Ficus subpisocarpa, a monoecious fig species studied in Taiwan. The ants feed on the mutualistic fig-pollinating wasps as well as on parasitic non-pollinating fig wasps. Nevertheless fig-wasps may not constitute a sufficient food source to ensure permanent presence of ants on the tree as the ants were observed to be frequently associated with hemipterans such as coccids and aphids. Fig wasps seem to constitute a reliable and sufficient food source on some dioecious Ficus species. On the contrary, in monoecious Ficus species, resident ants have always been observed to tend homopteran in addition to feeding on fig wasps. Frequent fruiting, prolonged fruit ripening period, ramiflory and rapid growth could constitute traits facilitating strong association based on fig-wasps' consumption of the monoecious F. subpisocarpa with ants. Despite these traits, ants were observed to tend hemipterans, and F. subpisocarpa does not seem to have evolved specialized morphological traits to facilitate the association.