Increased seed predation in the second fruiting event during an exceptionally long period of community-level masting in Borneo
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In Southeast Asian tropical rainforests, community-level masting (CM) occurs at irregular intervals of 2–10 years. During CM periods, many plant species from various families synchronously flower and subsequently undergo community-level fruiting. Seed predation is a key factor in understanding the ecological and evolutionary factors affecting CM. Masting is proposed to decrease seed mortality due to predation in two ways: by depressing predator abundance through extended and unpredictable absences of seeds; and by satiating predators via mass seed production (predator satiation hypothesis). If the hypothesis is valid in these rainforests, the incidence of seed predation will be higher in a fruiting event that occurs soon after a previous fruiting event, because the intervening period of seed absence would be inadequate to starve the predators. In this study, we examined seed predation by insects, focusing on five dipterocarp species that exceptionally reproduced twice during an extended CM period. All of the five species suffered more intense seed predation in the second fruiting event, consistent with the prediction expected from the predator satiation hypothesis. Weevils, bark beetles and mammals were the main cause of increased seed predation in three, one and one plant species, respectively. However, seed predation intensity did not increase during the second fruiting event in a few combinations of predator and plant species. We discuss the possibility that competition for seeds among predators and/or the interspecific differences in life history traits among predators might affect the varying intensities of seed predation among dipterocarp species by different seed predators.
KeywordsBornean lowland tropical rainforest Dipterocarpaceae General flowering Insect seed predators Predator satiation hypothesis
This study was conducted in accordance with memorandums of understanding signed in November 2005 by the Sarawak Forestry Corporation (SFC, Kuching, Malaysia) and the Japan Research Consortium for Tropical Forests in Sarawak (JRCTS, Sendai, Japan), and in December 2012 by the Sarawak Forest Department (SFD, Kuching, Malaysia) and JRCTS. We thank Joseph Kendawang, Mohd Shahbudin Sabki, Engkamat Anak Lading, and Mohamad bin Kohdi of SFD and Lucy Chong and Het Kaliang of SFC for their help in gaining permission to conduct the study. We also thank Tohru Nakashizuka (Tohoku University) for his support with our field study. This study was financially supported by Grants-in-Aid (No. 21255004 to T. I.) from the Japanese Ministry of Education, Science and Culture.
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