Frugivory, seed dispersal and gene flow of riparian figs in western Thailand

Fig trees (Ficus spp., Moraceae) are widely known as one of the most important plant genera in terms of providing food resources for wildlife. They also have an obligatory mutualism with fig wasps (Agaonidae), which makes fig trees a good subject to investigate coevolution between plants and animals. Many fig tree species are found in high humidity riparian areas, where some display adaptations for seed dispersal by water. However, the majority of research on fig tree seed dispersal has focused on big monoecious strangler fig tree species (Subgenus Urostigma), with few studies of smaller shrubby dioecious fig trees. This thesis aims to examine the vegetative and reproductive phenology of riparian fig tree species in Kanchanaburi Province, western Thailand including their interactions with terrestrial and aquatic frugivores, the function of a jelly-like substance produced by one species, and how gene flow has influenced the genetic structure of a second riparian fig tree. Also, current knowledge about global fig tree species and their interactions with vertebrate frugivores, based on published articles, is updated. The four riparian fig tree species studied are all evergreen. Figs of the dioecious F. oligodon, F. ischnopoda and F. montana were produced seasonally, with less seasonality of fig production in the monoecious F. racemosa. Fig production was likely to be influenced by temperature. Figs of F. racemosa were mostly produced towards the canopy level (more than 5 m above the ground), but the other three species tended to produce figs near to ground level. Most fig crops of the three dioecious species, which produced relatively smaller crop sizes than F. racemosa, were not visited by any frugivores during observation periods, and uneaten figs mainly fell to the ground or water. Where crops were visited, bulbuls (Pycnonotidae) were the most frequent frugivores visiting the small shrubs F. ischnopoda and F. montana and the Grey-bellied squirrel (Callosciurus caniceps, Sciuridae) were frequent visitors to the larger fig tree species (F. oligodon and F. racemosa). Figs that fell onto the water were consumed quickly by a fish, Blue mahseer (Neolissochilus stracheyi, Cyprinidae). However, seeds of F. montana ingested by this and another cyprinid fish (Barbonymus altus) were mostly destroyed, suggesting their roles are as seed predators rather than dispersers. A mucilaginous jelly covering F. oligodon seeds did not attract any ant species. Seeds covered with this jelly did not germinate, but could germinate rapidly once it was removed, suggesting its function is seed germination suppression and probably to protect the seeds from pathogens. Most genetic variation was within rather than between populations of F. montana, but extensive gene flow between populations was detected, generated mostly by pollen flow, because gene flow by seed dispersal was limited. This is consistent with the observations that very few frugivores interacted with this fig tree species. The global review of interactions between vertebrate frugivores and fig trees, which included data from this thesis, showed that the major frugivorous bird families that interact with fig trees are mynahs (Sturnidae), pigeons (Columbidae), bulbuls (Pycnonotidae) and parrots (Psittasidae), and the major families of frugivorous mammals were Old World monkeys (Cercopithecidae), Old World fruit bats (Pteropodidae) and New World fruit bats (Phyllostomidae). Strangler figs had the highest number records of frugivore species interactions, and few small dioecious species had any records of what eats their fruits. The limitations of the relevant literature outlined in an earlier (2001) review are unchanged, with recent records adding to the number of species records, but generally failing to add to a detailed understanding of how fig trees interact with frugivores.