Fruit Bat Seed Dispersal

The role of the fruit bat, Eidolon helvum, in seed dispersal, survival, and germination in Milicia excelsa, a threatened West African hardwood.

Daniel A. R. Taylor1, Bright O. Kankam2, and Michael R. Wagner1  

1Northern Arizona University, Flagstaff, Arizona; 2Forestry Research Institute of Ghana, Ghana, West Africa.

Evening Flight  

Eidolon's Evening Flight at the Kumasi Zoo

Abstract

Milicia excelsa isa valuable but threatened tropical hardwood. Frugivory and seed dispersal play an important role in tropical forest. We measured Milicia seed rain and conducted focal-tree observations and seed germination and predation trials to determine the importance of bats to Milicia seed dispersal. We conducted 300 hours of focal-tree observations at five fruiting Milicia trees. We measured seed rain using 56, 2-6 m2 seed traps totaling 200 m2, for 5,800 m2 trap nights. Traps were placed in canopy gaps in a 2 ha circular array at 3 distances from the focal tree. We conducted 7 germination trials using seeds that had passed through Eidolon'sdigestive tract, been spit out in rejecta pellets, extracted from fruit with pulp attached, and extracted from fruit, rinsed and dried. We recorded temporal and total germination rates. To test if Milicia seed predation rates differed significantly by density, distance to parent tree, or treatment category, we conducted 48 seed predation trials placing groups of 12 and 2 seeds treated as in the germination trials in small-medium canopy gaps at two distances from two focal trees. We recorded diurnal and nocturnal seed removal rates.

Bats accounted for >98% of Milicia seed dispersal and Eidolon visitation increased seed rain by more than 200%. No avian generated seed rain was recorded. Eidolon dispersed seeds appear to germinate faster and escaped seed predation longer than un-dispersed seeds. Bat dispersalmay be essential to the long-term survival of Milicia excelsa.