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 80 # 8 80 T. Nagamitsu and T. Inoue Sugar concentration (%) 50 T. collina T. fuscobalteata T. rufibasalis 40 T. melanocephala T. melina T. fimbriata 30 20 10 7:30 10:30 14:30 Time of day Figure 7.2. Temporal changes in sugar concentration (% total dissolved solids, per volume) of nectar loads for six Trigona (after Nagamitsu and Inoue 1998). Similarity (Cλ) 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 22-23 Jun 1994 10-13 Aug 1994 23-25 Sep 1994 15-18 May 1996 4-8 Aug 1996 19-23 Aug 1996 col-fus col-mli fus-mli col-mla fus-mla mla-mli Species pairs Figure 7.3. Pollen diet similarity (Morishita similarity index) at six periods in 1994 and 1996 in pairs of four Trigona species, T. collina (col), T. fuscobalteata (fus), T. melanocephala (mla), and T. melina (mli); after Nagamitsu et al. (1999b). 1 0 1
Name /sv04/24167_u07 10/27/04 05:27PM Plate # 0-Composite pg 81 # 9 7. Floral Resource Utilization by Stingless Bees 81 7.4 Mechanisms of Floral Resource Partitioning Floral resource utilization of Trigona species in LHNP showed preference in flower locations and floral shapes; it indicated partitioning of nectar and pollen between species that preferred different flower locations. Preferences in flower visitation may result from specific foraging traits, and matching between the foraging trait variation and floral resource heterogeneity may result in floral resource partitioning. Trigona melanocephala that preferred understory flowers was expected to forage the lowest stratum in the forest, whereas T. fuscobalteata was predicted to have the highest foraging stratum. To examine this prediction, we conducted field experiments three times using honey-water feeders that were vertically arranged at towers in LHNP (Nagamitsu and Inoue 1997b). In all three experiments, T. fuscobalteata did not visit the feeders frequently. Trigona melanocephala, however, frequently appeared in all the experiments, and always preferred the lowest feeders more than other feeders (see Fig. 7.4). Other Trigona and honeybees (Apis koschevnikovi) did not show stable patterns in foraging heights (Roubik et al. 1995, 1997). Possible factors for the variation in foraging heights are different physiological traits that fit sunny (canopy and gap) and shaded (understory) conditions. In La Selva, Costa Rica, Trigona species that visited Justicia aurea flowers differed between sunny and shaded places (Willmer and Corbet 1981). Trigona ferricauda and T. angustula (called jaty in that publication) preferred flowers in sunny places, whereas flowers in shaded places were visited by T. fulviventris, which was also more often caught in the understory than in the canopy in another light-trap study (Roubik 1993). These findings in La Selva and LHNP suggest that different foraging strata in relation to sunny and shaded conditions cause floral resource partitioning. Floral morphology determines accessibility to floral resources. Only flower visitors with long tongues obtain nectar secreted in the bottom of long, narrow corollas. Such morphological matching between floral parts and feeding organs is a major mechanism of floral resource partitioning. In general, in LHNP, T. erythrogastra preferred deep flowers and thus was expected to have longer tongues than the other species. To compare morphology among Trigona species in LHNP, we measured lengths of seven body parts in 17 species, and we performed discriminant analysis to separate these species based on the morphological characters (Nagamitsu and Inoue 1998). Seven characters were summarized in two variables and were plotted on a coordinate of the two variables (see Fig. 7.5). Trigona erythrogastra and T. thoracica were located far from the other species on vectors of tongue lengths (PL and GL), which indicates that the two species have the longest tongues relative to their body sizes. Although flower visits of T. thoracica were not recorded, a morphological match between T. erythrogastra and its visited flowers was found. In addition to the matching between foraging trait variation and floral resources, we found that aggressive interference caused temporal resource parti- 1 0 1
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7. Floral Resource Utilization by Stingless Bees (Apidae, Meliponini)

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