Journal of Tropical Ecology (2004) 20:421–427. Copyright © 2004 Cambridge University Press DOI: 10.1017/S0266467404001555 Printed in the United Kingdom Dispersal of Aglaia spectabilis, a large-seeded tree species in a moist evergreen forest in Thailand Shumpei Kitamura ∗1 , Shunsuke Suzuki†, Takakazu Yumoto ∗ , Pilai Poonswad‡, Phitaya Chuailua‡, Kamol Plongmai‡, Naohiko Noma†, Tamaki Maruhashi§ and Chumphon Suckasam¶ ∗ Center for Ecological Research, Kyoto University, Kamitanakami-Hirano, Otsu 520-2113, Japan † School of Environmental Science, The University of Shiga Prefecture, Hikone 522-8533, Japan ‡ Hornbill Project, Department of Microbiology, Mahidol University, Bangkok 10400, Thailand § Department of Human and Culture, Musashi University, Nerima, Tokyo 176-8534, Japan ¶ National Park, Wildlife and Plant Conservation Department, Bangkok 10900, Thailand (Accepted 30 June 2003) Abstract: We investigated the seed dispersal of Aglaia spectabilis, a large-seeded tree species in a moist evergreen forest of Khao Yai National Park in Thailand. Although one-to-one relationships between frugivores and plants are very unlikely, large-seeded plants having to rely on few large frugivores and therefore on limited disperser assemblages, might be vulnerable to extinction. We assessed both the frugivore assemblages foraging on arillate seeds of Aglaia spectabilis and dispersing them and the seed predator assemblages, thereby covering dispersal as well as the post- dispersal aspects such as seed predation. Our results showed that frugivores dispersing seeds were a rather limited set of four hornbill and one pigeon species, whereas two squirrel species were not dispersers, but dropped the seeds on the ground. Three mammal species were identified as seed predators on the forest floor. Heavy seed predation by mammals together with high seed removal rates, short visiting times and regurgitation of intact seeds by mainly hornbills lead us to the conclusion that hornbills show high effectiveness in dispersal of this tree species. Key Words: caching, camera trapping, frugivore, frugivory, hornbills, rodents, scatter hoarding, seed dispersal, seed predation, squirrels INTRODUCTION Compared with the flower–pollinator interaction, species- specific coevolution between a fruit species and a frugivore species is unlikely to occur; a diffuse coevolution between groups of plants and groups of dispersers is thought to be more typical (Herrera 1985, Wheelwright & Orians 1982). Indeed, studies of fruit–frugivore interactions investigated in several parts of South-East Asia demonstrate that it is typical for a number of frugivores to use the fruit of any particular plant species (Corlett 1998, Hamann & Curio 1999, Kitamura et al. 2002). However, there is a negative correlation between seed size and the number of observed frugivore groups, reflecting both the smaller number of large frugivore species and the ability of large frugivores to consume small fruits but not vice versa in South-East Asia (Corlett 1998, Hamann & Curio 1999, Heindl & Curio 1999, 1 Corresponding author. Email: shumpei@ecology.kyoto-u.ac.jp Kitamura et al. 2002, Noma & Yumoto 1997). Because of their requirements for survival, these large specialized frugivores are expected to be vulnerable to human impacts (Bennett & Robinson 2000, Corlett 2002, Peres 2000). In South-East Asia, increasingly, faunal assemblages have been shown to be reduced in many places, and it is possible that some plant species rely on a limited number of frugivore species (Corlett 2002). Thus, plants that produce large-sized seeds may be vulnerable to extinction when the populations of natural seed dispersers are diminished. The genus of tropical trees Aglaia (Meliaceae) produces arillate seeds dispersed by vertebrates in tropical Asia (Pannell 1992, Pannell & Koziol 1987). Hornbills are believed to be the principal dispersers of large-seeded dehiscent Aglaia species in Malaysia (Becker & Wong 1985, Pannell & Koziol 1987) and the Philippines (Hamann & Curio 1999, Heindl & Curio 1999). However, few of these studies were able to establish the effectiveness of hornbill seed dispersal for Aglaia species, even in terms of quantity (Schupp 1993). Furthermore, most studies,