Competition and Niche Overlap Between Gibbons (Hylobates albibarbis) and Other Frugivorous Vertebrates in Gunung Palung National Park, West Kalimantan, Indonesia

Abstract

Interspecific competition is considered to be one of the fundamental forces driving a wide range of evolutionary and ecological processes, but its importance in limiting mammalian populations has been hotly debated (Hairston et al. 1960; Fleming 1979; Schoener 1982; Walter and Paterson 1995). Early ecologists held the view that competition between species was of overriding importance in shaping vertebrate communities (e.g., Grant 1972; MacArthur 1972; Cody 1975; Diamond 1978). Others argued that interspecific competition was sporadic, and that its effects may be relatively unimportant compared to other ecological forces, such as climate or predation (e.g., Connell 1975; Wiens 1977; den Boer 1986; Post and Forschhamer 2002), and non-equilibrial and stochastic factors (e.g. Saether 1997; Hubbell 2001). Despite continued uncertainty over the precise nature of interspecific competition (Schoener 1982; Eccard and Ylonen 2003; Cooper 2004), few ecologists would deny that competition between species can have powerful effects on animal populations. Field experiments have demonstrated that the ecological effects of interspecific competition are widespread (reviewed in Connell 1983; Schoener 1983). Begon, Harper, and Townsend (1996: 800) concluded that competition ‘‘appears frequently to be important in vertebrate communities, particularly those of stable, species rich environments.’’ Most primates live in tropical rainforests, among the most stable and species rich environments on earth, suggesting that interspecific competition may be particularly important for these taxa. Primate field studies have indirectly inferred the importance of interspecific competition, either with primates or other vertebrate species. For example, density compensation—an increase in the density of one species in response to the decline in abundance of a competing species—has been reported in a wide