Growing Batty: UF/IFAS Researchers Discover That Rare Bats Pollinate Durian Trees
Every October, creatures of the night await their once-a-year opportunity to go forth and feast upon sweet treats offered abundantly throughout the neighborhood.
A typical Halloween in Florida? An event celebrating Bat Week, observed internationally Oct. 24-31? Not quite. The above paragraph describes Indonesian bat behavior, and it answers an ages-old question about how durian trees are pollinated on the island of Sulawesi, one of Indonesia’s largest.
For one graduate student with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), this research finding about how bats feed was the beginning of what she hopes will be a fairly short journey toward protecting her home country’s dwindling populations of flying foxes, a group that ranks among the world’s largest bats. Her findings appear in a paper published online this month by the journal Biotropica.
“Previous research studies had demonstrated that bats in Malaysia and Thailand helped pollinate durian trees, but we couldn’t assume that would be the case on Sulawesi as well, we needed to investigate,” said Sheherazade, who graduated in December 2018 with a master’s degree in wildlife ecology and conservation from the UF/IFAS College of Agricultural and Life Sciences (CALS). In keeping with Indonesian tradition, Sheherazade uses a single name.
The research was more than an academic exercise – durian trees yield a large, spiny fruit, also known as durian, which is tremendously popular in Southeast Asia. For many Indonesian farmers, durian trees are an integral part of their operations, and grow alongside other fruit trees including mango, rambutan and langsat. Indonesia’s durian exports are worth about $250 million annually, and the country is actually a net importer of the fruit.
“Because most durian in Indonesia is not planted in a monoculture plantation and there is still a lack of management to intensify production, production is quite low,” Sheherazade said. “In the area where we did the study, durian trees grow in a mixed plantation, and they do not get fertilizer or watering.”
Last year, Sheherazade spent four months in the western part of Sulawesi, beginning in October 2018, just before the durian trees bloomed. Each tree produces thousands upon thousands of pale, strongly scented, night-blooming flowers that harbor sweet nectar – a treat for Indonesia’s nectar-feeding bat species.
Durian trees generally do not self-pollinate, and it’s known that a variety of animals can contribute to the process by visiting the open blossoms, including moths, bees, bats and other mammals, Sheherazade said. To document pollinator activity in west Sulawesi, Sheherazade developed a simple but challenging study – with help from local men, the UF/IFAS research team would place video cameras high in durian trees, aiming the lenses at clusters of soon-to-bloom flowers.
After selecting suitable trees for camera placement, the team set up two experimental treatments and a control. One experimental treatment involved covering the flower clusters with a fine mesh fabric that would exclude any pollinators; the other involved covering flower clusters with mesh large enough to admit insects but not bats; the control group of flowers had no covering, providing access to all pollinators that approached.
“The video images showed three bat species visiting the blossoms, and they represented most of the pollinator activity,” Sheherazade said. “Two species of flying fox fed on nectar, and we documented a smaller bat species that visited the blossoms and accomplished some pollination as well.”
One honey bee species and one moth were also documented, she said.
By reviewing the video footage and then checking fruit-set that developed from the flower clusters under study, it was possible to show that very little fruit developed from the clusters that bats could not access, Sheherazade said. These results indicated that bats performed most of the durian pollination in the study area.
Flying foxes are among the wildlife species sought by “bushmeat” hunters, who slaughter large animals and sell the carcasses as meat. So, documented proof that flying foxes pollinate durian trees might help spur official action to protect the animals and their roosting habitat, she said.
“At least at the village to district level, people will grow more interested in protecting bats if they know the bats help produce durian fruit,” Sheherazade said. “I hope my research will increase active support from scientists and NGOs, now that it’s been published.”
Sheherazade’s UF/IFAS faculty adviser, bat expert Holly Ober, calls the project a strong example of work that illuminates an important connection between wildlife and human economic activity.
Ober, an associate professor with the UF/IFAS North Florida Research and Education Center in Quincy, noted that Florida’s native bat species do not feed on flower nectar, only insects.
“Indonesia has bat species that feed on insects, some that feed on nectar and some that feed on fruit,” Ober said. “Unfortunately, flying foxes will consume some local fruits, such as mango, in addition to nectar, which complicates efforts to protect them. Farmers sometimes put out poison to kill fruit-eating bats, and Sheherazade hopes to promote deterrent methods that don’t harm the bats but keep them away from fruit.”
Sheherazade also hopes that her call to bat conservation receives an enthusiastic response back home, because she sees durian as part of an entire way of life that goes back beyond memory.
“Many of the people (in Indonesia) now do not actually plant the durian on their farms, they inherited the trees along with the land from their grandparents,” she said. “It would be too troublesome now to convert the land to a durian-only plantation because the trees are often too big – they can reach 125 feet tall.”
For those unfamiliar with durian fruit, it’s a delicacy in Indonesia, Vietnam and neighboring countries, but little-known to U.S. consumers. Perhaps that lack of awareness stateside is partly due to the fact that raw durian has a very strong and pungent scent, leading to the nickname, “world’s smelliest fruit.”
Opinions don’t conflict, however, about durian’s nutritional benefits – high in fiber, monounsaturated fats and vitamin C.
Maybe one day it’ll catch on as a Halloween treat? Maybe not. Unless you’re a bat.