Interações entre plantas e beija-flores numa comunidade de Floresta Atlantica Montana em Itatiaia, Rio de Janeiro

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Studies of plant-pollinator interactions in vegetation communities can contribute to an understanding of evolutionary and ecological questions. This study sought to relate floristic composition, floral features, resource availability and hummingbird visitation in an ornithophilous assemblage in southeastern Brazil. During two years, data on life form, habitat, flowering phenology, floral morphology and biology, and visitors hummingbirds were obtained monthly in an area of montane Rainforest in the Parque Nacional do Itatiaia, RJ. We recorded 32 species in 15 families, with dominance of Bromeliaceae (34%), Gesneriaceae (16%) and Acanthaceae (9%), and prevalence of epiphytes and vines in the understorey. The most species presented annual flowering pattern and at the community level appears to occur the sequential pattern. In rainy period, one half of species was flowering, this period was often short, and medium corollas flowers predominated. In dry period, another half of species flowered, but their flowering time was bigger, and long corolla flowers were more common. Nectar volume values (standing crop) in open flowers were very low, and there was high intra and inter specific variation. These results become every species similar in relation to available quantities of resource, and indicate that hummingbirds need to visit a lot of flowers to fill their daily energetic requirements, favoring outcrossing. Standing crop of nectar bore little relationship to nectar production in terms of volume, as well as any significance was found between nectar availability and corolla length. However, there were differences among species in nectar sugar concentration and nectar production at anthesis beginning. In this period, hummingbirds experiment the flowers to define their daily visitation pattern, and such time corresponds also to phase of higher pollen availability in the most of species. All of these aspects may influence plant choices by foraging hummingbirds. These birds were predominant in the low strata, however, Trochilinae (Clytolaema rubricauda, Leucochloris albicollis and Thalurania glaucopis) were more common in the canopy than Phaethornithinae (Phaethornis eurynome and P. squalidus). Phaethornithinae visits predominated during the dry period while Trochilinae visits were too frequent in the wet period. Besides, differences in visitation frequency between morning and afternoon periods were verified, mainly between Phaethornithinae hummingbirds. The latter visited mainly species with medium and long corollas flowers, in a trapliner fashion. On the other hand, Trochilinae visited more species with short and medium corollas flowers, mainly as territorial. The most overlapping in resource use occurred between Phaethornis species. Pollen placement on the bill was predominant, however, it too occurred in other body parts, especially in Phaethornithinae, which pollinated the majority of the species. Phaethornis eurynome is the only resident hummingbird and can be considered the main pollinator, mostly of Bromeliaceae species. Hummingirds guild in the PNI is probably influenced by competition for floral resource because spatial, temporal, morphological and behavioral differences were recorded. Seasonality of flowering in species with different flower sizes may be an adaptive response to the different availabilities of hummingbird pollinators during the year. This in turn may relate to possible hummingbird migration movements between different altitudes at Itatiaia, depending on the intensity of the winter. Although richness and composition in the PNI ornithophilous flora are similar to other assemblages, this locality presented some peculiarities. Climate features, a quite influenced by altitude, appear play an important role in determining plant occurrence, flowering periods and also hummingbird species in a given site. These birds, on the other hand, exert influence about floral attributes of plants throughout the time by selection pressure

ASSUNTO(S)

beija-flor polinização mata atlantica itatiaia (rj) nectar

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