Adaptive phenology of Ficus subpisocarpa and Ficus caulocarpa in Taipei, Taiwan

Insect pollination is the main strategy used by Angiosperm plants to transport pollen to another individual. The interaction between entomophilous plants and their pollinators is often mutualistic, with many species pairs being interdependent. In obligate pollination mutualism, the plant relies on its partner for pollination, whereas the pollen vector relies on plant resources. In the mutualism between Ficus (Moraceae) and the fig wasps (Hymenoptera, Agaonidae), the plant provides oviposition sites to its exclusive pollinator, which has an extremely short lifespan (a maximum lifespan of few days). This study examined how fig trees maintain their associated pollinator populations by conducting a 45-month phenological survey of 27 and 64 trees belonging to the species Ficus caulocarpa and F. subpisocarpa in Taipei, Taiwan. The observations indicated that the trees produce figs year-round with no clear seasonal pattern, and are not affected by meteorological factors. On average, about 30% of the trees of both species were bearing figs during the survey. The duration of the fig development was longer during the winter-spring period than during the summer-fall period. The trees displayed strong asynchrony among trees in the population but each crop was synchronous within a tree. However, after wasp emergence, crops lost their synchrony with part of the figs ripening within few days whereas some figs only ripened eight weeks later for F. subpisocarpa and four weeks later for F. caulocarpa. This study also discusses the implications of fig frugivory and mutualism.