Abstract
On-going fragmentation of tropical forest ecosystems and associated depletion of seed dispersers threatens the long-term survival of animal-dispersed plants. These threats do not only affect biodiversity and species abundance, but ultimately ecosystem functions and services. Thus, seed dispersers such as the straw-coloured fruit bat, E. helvum, which traverse long distances across fragmented landscapes, are particularly important for maintaining genetic connectivity and colonizing new sites for plant species. Using high-resolution GPS-tracking of movements, field observations and gut retention experiments, we quantify dispersal distances for small- and large-seeded fruits foraged by E. helvum during periods of colony population low (wet season) and high (dry season) in an urban and a rural landscape in the forest zone of Ghana. Gut passage time averaged 116 min (range 4–1143 min), comparable to other fruit bats. Movements were generally longer in the urban than in the rural landscape and also longer in the dry than in the wet season. As the majority of seeds are dispersed only to feeding roosts, median dispersal distances were similar for both large (42–67 m) and small (42–65 m) seeds. However, small seeds were potentially dispersed up to 75.4 km, four times further than the previous maximum distance estimated for a similar-sized frugivore. Maximum seed dispersal distances for small seeds were almost twice as long in the rural (49.7 km) compare to the urban (31.2 km) landscape. Within the urban landscape, estimated maximum dispersal distances for small seeds were three times longer during the dry season (75.4 km) compared to the wet season (22.8 km); in contrast, distances in the rural landscape were three times longer in the wet season (67 km) compared to the dry season (24.4). Dispersal distances for large seeds during the dry season (551 m) in the rural landscape were almost twice that in the wet season (319 m). We found no influence of food phenology on dispersal distances. The maximum likelihood for seed dispersal beyond feeding roosts (mean distance from food tree 263 m) was 4.7%. Small seeds were dispersed over even longer distances, >500 and >1000 m, with a likelihood of 3.0 % and 2.3 % respectively. Our data show that E. helvum retains ingested seeds for very long periods and may traverse large distances, probably making it an important long distance seed disperser in tropical Africa. We suggest E. helvumis important for ecosystem functioning and urge its conservation.
Highlights
Seed dispersal affects many key aspects of plant biology, including vegetation structure and composition as well as the diversity and dynamics of plant communities and meta-populations
Fruit bats are prime candidates in this regard, as their ability to fly over long distances during foraging makes them suited for this role (Shilton et al, 1999; Richter and Cumming, 2006; Tsoar et al, 2010)
Our study showed that E. helvum may potentially disperse seeds over a modest median of 42–67 m, and up to a maximum of 75.4 km, which is four times farther than the previously highest maximum distance of 20 km estimated for the Egyptian fruit bat (Rousettus aegyptiacus) (Tsoar et al, 2010)
Summary
Seed dispersal affects many key aspects of plant biology, including vegetation structure and composition as well as the diversity and dynamics of plant communities and meta-populations. Fruit bats are prime candidates in this regard, as their ability to fly over long distances during foraging makes them suited for this role (Shilton et al, 1999; Richter and Cumming, 2006; Tsoar et al, 2010). They are important pollinators and seed dispersers for a large number of plants of high ecological and economic value (Fujita and Tuttle, 1991; Muscarella and Fleming, 2007; Kunz et al, 2011; Seltzer et al, 2013; Scanlon et al, 2014)
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