How efforts to understand origins and diversity led to efforts to conserve and protect the world’s largest bats
COVER STORY 47(2):
Tsang, SM, Wiantoro, S, Veluz, MJ, et al. (2020) Dispersal out of Wallacea spurs diversification of Pteropus flying foxes, the world’s largest bats (Mammalia: Chiroptera). J. Biogeography 47(2): 527– 537. https://doi.org/10.1111/jbi.13750
Long-distance dispersal (LDD) is often regarded as a rare and unpredictable event, causing some to consider it an untestable hypothesis. However, advances in genomics, niche modeling, and computation enable direct and indirect testing of LDD hypotheses, particularly in understanding the evolution of recently diverged taxa. These studies have primarily been conducted on plants and a handful on bird groups, but the role of dispersal in bat diversification is scarcely studied. Historically, research on Paleotropical bats has lagged behind other vertebrates, but recent capacity-building efforts have enabled internationally collaborative research in Southeast Asia. Studying LDD in flying foxes, the world’s largest bats in the genera Pteropus and Acerodon, is difficult because some widespread species are found in more than half a dozen countries, while numerous endemic species are restricted to individual islands or island groups from American Samoa to Zanzibar. By assembling a multi-national team for locating and sampling tissues from these rare bats, we were able to conduct one of the first biogeographic studies of a species-rich mammal taxon in the Indo-Australian Archipelago (IAA).
The IAA is a fascinating biogeographic laboratory, as the fission and fusion of landmasses over geologic time have both isolated and re-connected areas in rapid succession. Biotic studies in the IAA are few relative to that of other tropical areas, particularly in Wallacea, the area between Borneo and New Guinea. Many islands in Wallacea have never been connected to a continent. Our study suggests that Pteropus originated in Wallacea at a time when the relatively depauperate ecosystems on recently formed islands presented “blank canvases” to which flying foxes dispersed and subsequently diverged from their ancestors. For the most part, the number of flying fox species found in an area seems unaffected by the size of the bat, the distance between islands, or the age of the lineage (with a possible exception in the South Pacific). Flying foxes can carry fruits, swallow seeds whole, and fly nearly 90 km in an evening, potentially over water. They are acknowledged as crucial seed dispersers in the rainforest where they occur, but their impact on plant historical biogeography and diversification, through co-dispersal, for example, is little studied.
During the course of fieldwork for this study, members of our team located bat species that hadn’t been seen alive in over two decades. We also found that colony sizes are shrinking throughout the IAA; a colony’s crepuscular emergence no longer blankets the sky with black, leathery wings. We observed that species throughout Asia are hunted at unsustainable levels for human consumption, which creates a conservation crisis for bats and a public health hazard for humans, who could be exposed to potentially lethal pathogens. This has motivated us to train multiple grass-roots organizations and local scientists in standardized population monitoring and outreach methods, along with push for localized hunting bans or regulations to prevent further decline. Expansive biogeographic studies like this may not be possible in the future if the current rate of population extirpation continues. Flying foxes and other fruit bats are charismatic but little known. They are perhaps best studied in Australia where roosts are near urban areas, but only 5 of the 65 known species are found there. A majority of species are endemic to single islands or island groups, and these species are understudied, despite their importance for forest regeneration on isolated, oceanic islands. Future studies will examine the environmental impact of flying foxes on terrestrial and marine ecosystems, as many species roost in large aggregates in liminal areas, such as mangroves, that abut vulnerable ecosystems such as coral reefs.
Written by: Susan M. Tsang (1) & David J. Lohman (2)
(1) Research Associate, Department of Mammalogy, American Museum of Natural History; Research Associate, Mammalogy Section, Philippine National Museum of Natural History.
(2) Associate Professor, Department of Biology, City College of New York & PhD Program in Biology, Graduate Center, City University of New York; Research Associate, Entomology Section, Philippine National Museum of Natural History (Philippines).
Adult Pteropus vampyrus from Bali, Indonesia.