PALAVRAS-CHAVE: Ecologia, Polistinae, manguezal, restinga, Mata AtlânticaABSTRACT -We studied the structure and composition of communities of social wasps associated with the three insular ecosystems: mangrove swamp, the Atlantic Rain Forest and the ´restinga´-lowland sandy ecosystems located between the mountain range and the sea. Three hundred and ninety-one nests of 21 social wasp species were collected. The diversity of wasps found in each ecosystem was significantly correlated to the diversity of vegetation in each of the three physiognomies, (r 2 = 0.85; F(1.16) = 93.85; P < 0. 01). The Tropical Atlantic Forest physiognomy had higher species richness (18 species), followed by the restinga (16 species) and the mangrove (8 species) ecosystems.

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The Africanized honeybee Apis mellifera (AHB) is an invasive species spread over all Brazilian biomes, which has negative impacts on native bee populations, but whose impacts on native plants are still controversial. In order to understand how its impacts extend to the pollination service at the community level, we studied the AHB and its interactions in a multi-species context using network theory. We analyzed six pollination networks from the Brazilian Caatinga, a xeric biome where beekeeping is increasing very quickly. The AHB occupied a central position in all networks, as it was responsible for a large share of the interactions observed (14 ± 7 %) and bound together different modules. By simulating the removal of the AHB from each network, we observed no effects on connectance, but a strong decrease in nestedness (-23 ± 19 %) and an increase in modularity (8 ± 5 %). The robustness of networks to cumulative random extinctions was on average not affected. In summary, our evidence points out that the AHB induces significant changes in the structure of native pollination networks, mainly by making them more cohesive and monopolizing many interactions. Although the AHB did not affect network robustness, its net impact on the pollination service may be negative, because this invasive species is very generalistic and may not be an efficient pollinator for some native plants.

-Wasps and bees are important components of fl ower visitor guilds in the Neotropical region. The abundance of social wasps and bees, collected during fl ower visits, was used to calculate niche breadth and niche overlap indices, in order to characterize the utilization of the fl oral resources by those insects. Samples were taken monthly, for 13 months (156h), by two collectors which captured the specimes on fl owers using entomological nets, while walking along a way in an area of caatinga at Itatim, State of Bahia, Brazil. Wasps and bees heavily visited a few sources of fl oral resources, but the most visited plants by each group were different, and few plant species were important for both groups, resulting in low niche overlap between bees and wasps. The niche overlap among wasp species was generally higher than among bee species. The general overlap, which takes into consideration all species together was low (< 30%).KEY WORDS: Niche, overlap, fl ower visitor, semi-arid region RESUMO -Vespas e abelhas são importantes componentes da guilda de visitantes fl orais nos Neotrópicos. A abundância de vespas sociais e abelhas visitando fl ores foi utilizada para calcular os índices de amplitude e sobreposição dos nichos trófi cos e para caracterizar o uso das fontes de recursos fl orais por aqueles insetos. A amostragem foi realizada mensalmente, durante 13 meses (156h), por dois coletores que capturaram os espécimes com redes entomológicas, ao longo de uma trilha em uma área de caatinga em Itatim, BA. As vespas e abelhas concentraram as visitas em poucas fontes de recursos. As plantas mais visitadas por cada um desses grupos foram distintas e poucas espécies de plantas foram importantes para ambos os grupos, resultando em baixos índices de sobreposição entre abelhas e vespas. A sobreposição do nicho trófi co entre espécies de vespas foi em geral mais elevada do que entre espécies de abelhas. A sobreposição geral entre todas as espécies foi baixa (< 30%).PALAVRAS-CHAVE: Nicho, sobreposição, visitante fl oral, região semi-árida

Trophic niche breadth and niche overlap of bees were studied in a region of Caatinga (a deciduous dry thorn scrub forest) in Brazil with the lowest mean annual rainfall of the country, highly seasonal environmental variation, and an unpredictable rainy season. A null model approach was used to determine if the observed niche overlap in the community differed from that expected by chance. In general, even bee species with wider trophic niches concentrated foraging efforts on flowers of only a few of the available plant species, with low trophic niche overlap between pairs of species and among all species in the community. A randomization test showed niche overlap among the 10 common species in the guild to be significantly less than expected by chance, suggesting the existence of functional complementarity. The structure of communities defined by high functional complementarity is likely to be more sensitive to variation in available resources (e.g., richness and abundance of floral resources for bees). Ecosystem services provided by such communities may be more greatly affected by environmental changes (anthropogenic activities and climate change) than are services provided by communities with greater functional redundancy. stingless bees / Apoidea / solitary bees / Caatinga / semiarid / niche overlap

The social wasp nests were quantified in three different plant physiognomies (forested Caatinga, shrubby Caatinga, and agricultural systems) to analyze the effect of environmental seasonality and plant physiognomy on the richness, nest abundance, and species composition of social wasps in the region of tropical dry forest of Brazil. The forested Caatinga physiognomy had the greatest richness of species (S = 16), followed by shrubby Caatinga (S = 13) and by agricultural system (S = 12). The first axis of detrended correspondence analysis (DCA) explained 67.8% of the variability and shows a gradient of the fauna from agricultural system and shrubby Caatinga to forested Caatinga. In the first axis, wet season scores were much higher than those for the dry season in forested Caatinga. The second axis explained 18.7% of the variability and shows a separation of samples collected during the wet or the dry periods in shrubby Caatinga. This separation was less evident in the agricultural system. Variations in nest abundance were more intense in arbustive caatinga (45% decrease in number of active nests in the dry period), moderate in forested Caatinga (24% decrease in number of active nests in the dry period), and low in agricultural systems (8% decrease in the dry period).