Abstract
Ficus species are keystone plants in tropical rainforests, and hemi-epiphytic figs play a notably important role in forest ecosystems. Because hemi-epiphytic figs have strict germination requirements, germination and establishment stages regulate their populations. Despite the ecological importance of hemi-epiphytic figs in the rainforests, seed dispersal systems by fig-eating animals under natural conditions remain unknown because of the difficulty in tracing the destiny of dispersed seeds in the canopy. Therefore, seed dispersal effectiveness (SDE) has never been evaluated for hemi-epiphytic figs. We evaluated the SDE of hemi-epiphytic figs using qualitative and quantitative components by three relatively large-sized (> 3 kg) arboreal and volant animals in Bornean rainforests that largely depend on fig fruits in their diets: binturongs Arctictis binturong, Mueller’s gibbons Hylobates muelleri, and helmeted hornbills Rhinoplax vigil. The SDE values of binturongs was by far the highest among the three study animals. Meanwhile, successful seed dispersal of hemi-epiphytic figs by gibbons and helmeted hornbills is aleatory and rare. Given that seed deposition determines the fate of hemi-epiphytic figs, the defecatory habits of binturongs, depositing feces on specific microsites in the canopy, is the most reliable dispersal method, compared to scattering feces from the air or upper canopy. We showed that reliable directed dispersal of hemi-epiphytic figs occurs in high and uneven canopy of Bornean rainforests. This type of dispersal is limited to specific animal species, and therefore it may become one of the main factors regulating low-success hemi-epiphytic fig recruitment in Bornean rainforests.
Highlights
Ficus (Moraceae) is one of the world’s largest woody plant genera with approximately 750 species of various growth forms: trees, shrubs, climbers, epiphytes, and hemi-epiphytes [1]
Binturongs, Mueller’s gibbons, and helmeted hornbills fed on whole fig fruits, while several consumers, such as long-tailed macaques, pigeons, squirrels, and barbets often partially consumed fig fruits
The mean feeding speed of binturongs, gibbons, and helmeted hornbills was 11.69 ± 10.91 (n = 5), 9.21 ± 4.64 (n = 8), and 6.19 ± 2.81 (n = 5), respectively; the estimated number of fig fruits consumed in a fig patch per day was 1063.47, 309.45, and 58.16, respectively; and the estimated ingested seed number in a fig patch per day was 132640.4, 31554.1, and 8713.8, respectively (Fig 1)
Summary
Ficus (Moraceae) is one of the world’s largest woody plant genera with approximately 750 species of various growth forms: trees, shrubs, climbers, epiphytes, and hemi-epiphytes [1]. This fruiting pattern enables obligate pollination mutualism with wasps (Agaonidae) by maintaining the pollinating wasp population [4] Because of their year-round fruiting patterns, Ficus species are considered keystone food resources for animals in tropical rainforests, especially when the availability of preferred fruits is low [3,5,6,7]. Among the Ficus species, hemi-epiphytes include approximately 300 species [1] and occupy one-third to over one-half of the fig species in the rainforest community [8] They are a major component of canopy ecosystems across tropical regions [9], and they increase population turnover and forest regeneration by causing host tree-fall [10]. Hemi-epiphytic figs play a notably important role in forest ecosystems
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