Fruiting phenology affected by seed preference and fluctuation of seed predator activity in a Tropical Peat Swamp Forest

Abstract

The hypothesis that the fruiting phenology of a plant community is affected by both fluctuating predation pressure and the seed preference of predators (risk of predation) was tested in a tropical peat swamp forest in Central Kalimantan, Indonesia. We conducted: (i) a seed removal experiment using model seeds (i.e. jackfruit seeds which are low in secondary compounds and attractive to seed predators) that investigated fluctuations in predators' activity and (ii) a seed removal experiment using 17 natural species to clarify seed preferences of seed predators; we also monitored the fruiting phenology of the 17 study species. The removal rate of model seeds decreased during high water table, whilst it increased during low water table, indicating that flooding restricted the feeding activity of terrestrial small mammals which are the dominant seed predators in peat swamp forest. Differences in fruiting time between species with higher removal rates (preferred) and lower removal rates (less preferred) were observed. Species with high removal rates showed peaks of fruiting during flood periods and the reproductive pattern of this group was negatively regressed to the removal rate of model seeds and positively regressed to water level. The implication of this result is that these tree species produce seeds and deposit them on the ground whilst seed predators are disturbed by flooding, thus they avoid seed deposition when predators' activity is high. Seed production amongst species with low removal rates was variable indicating that these tree species are likely more adapted to other factors that affect survival of seeds and/or seedling (i.e. regeneration niche) than predation. We were able to demonstrate another relationship between fruiting phenology and seed predation that differs from that of mast fruiting. The fact that species with preferred seeds produce their fruits when predator activity is restricted might have developed under the conditions of poor nutrient availability and frequent flooding that are characteristic of the peat swamp forest ecosystem.