7. Floral Resource Utilization by Stingless Bees (Apidae, Meliponini)

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Name /sv04/24167_u07 10/27/04 05:27PM Plate # 0-Composite pg 74 # 2 74 T. Nagamitsu and T. Inoue tropical rain forests. In La Selva, Costa Rica, medium-sized bees that include meliponine, halictid, and megachilid bees are believed to pollinate 14% of plant species (Kress and Beach 1994). In Lambir, social bees that include honeybees, stingless bees, and the subsocial allodapine bees (small carpenter bees that make nests in stems) apparently pollinate the largest number (32%) of plant species (Momose et al. 1998c). However, interaction between plants and stingless bees is not only mutualistic but also antagonistic. Nectar and pollen robbing by stingless bees reduces reproductive success of many plants (Roubik 1982, 1989). Stingless bees are generalist foragers and may visit flowers of more plant species than coexisting solitary bees and wasps (Heithaus 1979). Plant taxa of nectar and pollen sources are shared among stingless bee species as well as between stingless bees and honeybees (Koeniger and Vorwohl 1979; Roubik et al. 1986; Wilms and Wiechers 1997; Eltz et al. 2001). Such generalized utilization of common resources results in interference and exploitative competition that reduces not only foraging efficiency at feeding patches (Johnson and Hubbell 1974; Roubik 1980) but also pollen and nectar harvest of colonies (Roubik et al. 1986; Wilms and Wiechers 1997). Availability of either foods or nest sites is likely to limit population density of stingless bees (Hubbell and Johnson 1977; Inoue et al. 1993; Eltz et al. 2002). Effects of competition on population density, however, have not been well confirmed (Roubik 1983; Roubik and Wolda 2001). Different foraging strategies also allow stingless bee species to share the same type of resources by partitioning them in different times and places (Johnson 1982). These foraging strategies differ according to variation in foraging traits, such as body size, energetic cost of foraging, aggressiveness, communication, and recruitment. With respect to variation in aggressiveness, two mechanisms have been proposed for resource partitioning. First, the more aggressive species monopolize clumped and rich resources, whereas the less aggressive species are excluded from the resources and forage on scattered or poor resources (Johnson and Hubbell 1975; Johnson 1981). Second, early-arriving, less aggressive species are temporally replaced with late-arriving, more aggressive species, because more aggressive species require more time to discover new resources than do the less aggressive ones (Hubbell and Johnson 1978). Aggressive foraging behavior of stingless bees has been rarely investigated in Asia. Behavior of stingless bees and honeybees at artificial feeders was observed in Sri Lanka (Koeniger and Vorwohl 1979) and Peninsular Malaysia (Khoo 1992). Koeniger and Vorwohl (1979) suggested that aggression of stingless bees compensated for disadvantage due to smaller foraging area of stingless bees than that of honeybees. Khoo (1992) observed that more aggressive species that arrived later at feeders excluded less aggressive species that had already visited the feeders. These studies, however, were conducted using both artificial and highly concentrated resources and were not designed to examine how aggressiveness affects the partitioning of floral resources. Frequent partitioning of common resources by foraging in different times and places may be a unique feature of social insects, which often evaluate changing resource availability as they communicate the locations of optimal feeding sites 1 0 1
Name /sv04/24167_u07 10/27/04 05:27PM Plate # 0-Composite pg 75 # 3 7. Floral Resource Utilization by Stingless Bees 75 (Seeley 1995, Davidson 1998). However, there are also other factors that may enable stingless bee species to partition floral resources among plant taxa having different floral traits. A lowland mixed-dipterocarp forest in LHNP has extremely high tree species richness (LaFrankie et al. 1995), which is suitable to study partitioning of a wide taxonomic range of floral resources. Because the architecture of lowland mixed dipterocarp forests is complex (Ashton and Hall 1992), stingless bees may partition flowers in different locations in the forest. Furthermore, flowers of different taxa are morphologically diverse, and thus stingless bee species may specialize on flowers of a particular morphology. Previous studies of flower visits and pollen diets of stingless bees have not been well designed to detect partitioning in relation to such variation in floral features. Another characteristic of lowland mixed dipterocarp forests is general flowering (Ashton et al. 1988). General flowering (GF) may have great importance to the population and behavior of pollinators, caused by changing availability of floral resources. In Panama, the El Niño-southern oscillation produced a floral resource flush in the dry season, followed by an increase in bee populations (Roubik 2001). In Malaysia, specific responses of some pollinators, such as thrips, chrysomelid beetles, and giant honeybees, have been proposed. Thrip populations rapidly increase due to their short generation time and high fecundity (Appanah and Chan 1981). Giant honeybees immigrate to lowland mixed dipterocarp forests as soon as general flowering starts, and when it finishes they leave these particular forests (Itioka et al. 2001a). Stingless bees, however, show none of these responses, i.e., rapid population growth (Inoue et al. 1993), changes in food types (Nagamitsu and Inoue 2002), or migration over a long distance (Inoue et al. 1984a). 7.2 Stingless Bees in Lambir Hills National Park The taxonomy of stingless bees of Southeast Asia has advanced due to an early foundation (Schwarz 1937, 1939), excellent revisions (Sakagami 1975, 1978), and the relatively small number of species. In Asia and the Sunda islands, there are three genera, Trigona, Pariotrigona, and Lisotrigona, and three subgenera, Lepidotrigona, Homotrigona, and Heterotrigona in the genus Trigona—as shown in Table 7.1 and Plate 9 (Michener 2000). There have been different systems for classifying stingless bees (Moure 1961; Wille 1979). Although these systems are still modified, an intermediate system of special interest for studies in Southeast Asia was presented (Sakagami 1982), as follows: In the subgeneric system of Sakagami (1982), the subgenus Heterotrigona in Michener (2000) was further divided into eight subgenera and five species groups. A key to workers of the Sumatran species, which includes most of the regional species, is available (Sakagami et al. 1990). The distribution of Indo-Malayan stingless bees is described based on records from 10 localities and collections of the Canopy Biology Program in Sarawak, or, CBPS (see Table 7.1). CBPS collected 25 species in six locations throughout 1 0 1
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7. Floral Resource Utilization by Stingless Bees (Apidae, Meliponini)

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