Composition of frugivores of Baccaurea ramiflora (Phyllanthaceae) and effects of environmental factors on frugivory in two tropical forests of China and Thailand

摘要

Frugivory and seed dispersal are key processes that shape both plant and animal communities, they are important in the maintenance and regeneration of forest ecosystems while threatened by environmental changes. This study investigated the frugivores and environmental factors affecting animal visitation and fruit consumption of the evergreen tree Baccaurea ramiflora (Lour.) in Chinese (Xishuangbanna) and Thai (Mo Singto) tropical forest plots. The two plots differ in their mammal faunas, with more large species (Asian elephant, white-handed gibbon, bears) surviving on the Mo Singto plot. We asked whether these differences could resulted in different seed dispersal patterns on the two plots. Nine individual trees were selected in each plot to record arboreal and ground frugivores of B. ramiflora using camera traps. A total of 27 frugivore species were captured from both forest plots, 15 species in Xishuangbanna and 22 in Mo Singto, with ten species shared in both plots. The major frugivores of B. ramiflora in Xishuangbanna were all pre-dispersal seed predators with little contribution to seed dispersal, including Palla’s squirrel ( Callosciurus erythraeus ), red-cheeked squirrel ( Dremomys rufigenis ) and black giant squirrel ( Ratufa bicolor ). Meanwhile, the major frugivores in Mo Singto were two effective seed dispersers pig-tailed macaque ( Macaca leonina ) and white-handed gibbon ( Hylobates lar ), and seed predator black giant squirrel ( Ratufa bicolor ). The diversity and body size of frugivores in the Xishuangbanna plot were relatively small compared with those in Mo Singto plot. Small-bodied frugivores showed higher activity in Xishuangbanna plot whereas relatively larger frugivores were most active in the Mo Singto plot. The environmental factor that consistently influenced frugivore activity (visitation and consumption of B. ramiflora fruits) was fruit abundance. Ground cover was also a predictor for average visit length and fruit consumption of frugivores. Frugivores visitation rate was higher in Xishuangbanna while average visit length and consumption rates were higher in Mo Singto. The defaunation of large body-size frugivores in Xishuangbanna could have been a result of habitat loss and higher hunting pressure. This may lead to shorter dispersal distances for large-seeded plants, restricting their ability to move across changing landscapes, and threatening their chances of survival over the long term.