PARENT SESSION
Oral Session #81: Pollination and Dispersal.
Presiding: T. Ricketts
Thursday, August 8. 9:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.
Seed dispersal by flying foxes: evidence for a threshold effect in a Polynesian rain forest.
Drake, Donald*,1, McConkey, Kim2, 1 University of Hawaii, Honolulu, HI2 Victoria University of Wellington, Wellington, New Zealand
ABSTRACT- Due to historical extinctions of large avian frugivores, flying foxes (Pteropus spp. fruit bats) are now the main dispersers of large seeds in the shrinking rain forests of parts of the South Pacific. Most flying foxes swallow seeds <5 mm in diameter, but spit out larger ones. Some species aggressively defend feeding territories in fruiting trees. When flying fox abundance is low, interactions are uncommon, and a feeding animal is likely to remain in a single tree, dropping seeds directly beneath it. When flying fox abundance increases, animals in fruiting trees repel newcomers, who may snatch a fruit to eat elsewhere, thus dispersing the seeds. We investigated how the abundance of Pteropus tonganus affects patterns of seed dispersal on a series of islands in Tonga that supported a range of abundances of flying foxes and fruits. Fruit abundance placed an upper limit on the abundance of foraging animals; islands with few fruiting trees had few flying foxes, but islands with many fruiting trees had either few or many flying foxes. We compared flying fox abundance indices (animals h-1 transect-1 divided by relative density of fruiting trees) and patterns of seed dispersal; this revealed the threshold abundance at which foraging animals must occur in order to initiate social interactions and achieve high rates of seed dispersal. At abundance indices from 0-0.6, a constant 17% of the seeds that flying foxes handled were dispersed away from fruiting trees. As the index increased from 0.6-1.1, the percentage of seeds dispersed increased linearly to 50%. Understanding the non-linear relationship between bat abundance and seed dispersal is important for the conservation and management of forests that rely on these animals for seed dispersal.
KEY WORDS: Pteropus, seed dispersal, Pacific, conservation