Abstract
Flying foxes (Pteropodidae) are key seed dispersers on the African continent, yet their migratory behavior is largely unknown. Here, we studied the movement ecology of the straw-colored fruit bat, Eidolon helvum, and other fruit bats by analyzing stable isotope ratios in fur collected from museum specimens. In a triple-isotope approach based on samples of two ecologically similar non-migratory pteropodids, we first confirmed that a stable isotope approach is capable of delineating between geographically distinct locations in Sub-Saharan Africa. A discriminant function analysis assigned 84% of individuals correctly to their capture site. Further, we assessed how well hydrogen stable isotope ratios (δ2H) of fur keratin collected from non-migratory species (n = 191 individuals) records variation in δ2H of precipitation water in sub-Saharan Africa. Overall, we found positive, negative and no correlations within the six studied species. We then developed a reduced major axis regression equation based on individual data of non-migratory species to predict where potentially migratory E. helvum (n = 88) would come from based on their keratin δ2H. Across non-migratory species, δ2H of keratin and local water correlated positively. Based on the isoscape origin model, 22% of E. helvum were migratory, i.e. individuals had migrated over at least 250 km prior to their capture. Migratory individuals came from locations at a median distance of about 860 km from the collection site, four even from distances of at least 2,000 km. Ground-truthing of our isoscape origin model based on keratin δ2H of extant E. helvum (n = 76) supported a high predictive power of assigning the provenance of African flying foxes. Our study highlights that stable isotope ratios can be used to explain the migratory behavior of flying foxes, even on the isotopically relatively homogenous African continent, and with material collected by museums many decades or more than a century ago.
Highlights
Flying foxes are central ecosystem service providers in the Old World [1,2]
We focused on E. helvum (n = 88 individuals) which is assumed to migrate over large parts of the sub-Saharan African continent, and as a reference we selected six likely non-migratory pteropodid species: Rousettus aegyptiacus (n = 34 individuals), Lissonycteris angolensis (n = 17), Epomophorus wahlbergi (n = 23), Hypsignathus monstrosus (n = 30), Epomops franqueti (n = 30), and Epomophorus crypturus (n = 57)
To assess the migratory behavior of flying foxes based on stable isotope ratios measured in museum specimens, we modeled the origin of E. helvum using their individual d2HK values, as outlined in [27] and modified from [29] where each value of d2HK was associated to a location according to the African isoscape of hydrogen [45]
Summary
Flying foxes (family Pteropodidae) are central ecosystem service providers in the Old World [1,2]. More than 280 plant species benefit from flying foxes either by pollination and/or seed dispersal. Flying foxes are essential for maintaining the genetic connectivity of plants among fragmented patches of rainforests and distant habitats due to their capability to move over long distances [5,6,7]. Pteropodids play a prominent role as a reservoir for zoonotic diseases [8,9,10,11]. We looked at the movement ecology of Eidolon helvum to better understand their potential role in the large-scale distribution of seeds across the African continent and to shed light on the spatial use of flying foxes in context to zoonotic diseases.
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