DENSITY-DEPENDENT SEED PREDATION AND PLANT DISPERSION OF THE TROPICALPALM NORMANBYA-NORMANBYI

We measured the response of seed predators to variation in seed densit y and distance between seed sources of palms in North Queensland, Aust ralia. Adult palm trees occurred at a density of 20/ha. Their distribu tion was highly dumped and more than half the immature plants occurred within 3 m of an adult. Adult palms were also arranged in lines down the slope, apparently reflecting patterns of seed carriage by overland water flow. Seed dispersal is also affected by cassowaries, a ratite which ranges over many hundreds of ha and deposits seeds in dusters. S mall mammals which range over a few ha may deposit seeds as single ent ities (singletons). Many seeds remain undispersed beneath the female p arent with heavy predation. In this study seeds were placed beneath ad ult trees at two densities and were dispersed over varying distances a s clusters of ten seeds and as singletons. Pigs and earwigs were the p rincipal predators but they did not destroy all the seeds in any treat ment. However, the germination percentage of the remaining seeds was g reatly depressed indicating that one or both predators were disproport ionately selecting potential germinants. Pigs were responsive to both density of seeds beneath a tree and the distance between seed sources; they did not damage dispersed seeds to a great extent. Earwigs also d estroyed seeds more heavily beneath adult trees, but they were more ef ficient than pigs at locating dispersed seeds. Rodent predation was li ght and not responsive to seed density or dispersal.