Influencia da variação fisionomica da vegetação sobre a composição de aves frugivoras na Mata Atlantica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

Due to the alarming rate of deforestation in tropical forests, a better understanding on the organization of biological communities is needed, specifically regarding the interactions between birds and plants. Although this aspect is not often included among the top priorities for biodiversity conservation, it must be considered an important of effort in the attempts to maintain functional communities and to guarantee the continuing of species interactions over time. The spatial and temporal variation on bird abundance was studied in different habitats of Atlantic Forest, from April 1999 to March 2002, in order to answer the following questions: 1) What of these factors could more affect bird abundance and species richness in the Atlantic Forest habitats: vegetation structure, plant species composition or fruit abundance? 2) What are the effects of the temporal and spatial variation of the fruit abundance and quality on frugivorous bird abundance? 3) How do frugivorous birds selected fruits in relation to morphology and nutritional composition? Is there any relationship between fruit species richness and fruit morphology or fruit quality? To answer these questions, five sample units were set in each habitat, each consisting of one line of mist nets associated with three adjacent plots where bird captures were conducted along with the recording of phenological and vegetational structure data. The vegetation structure was characterized by the following variables: total height, lower crown height, diameter at breast height and frequencies of plant habits. In monthly field trips, plants inside the plots were examined for the presence of zoochorous ripe fruits and birds were mist-netted. Information about interactions between birds and plants were obtained by the occurrence of seeds in fecal samples of captured birds, as well as by recording their feeding behavior. All ripe fruits found in each habitat were measured and their pulp collected for chemical analyses. Results indicate that bird communities were sensitive to the variation in floristic and vegetation structure among habitats and showed particular preference for some specific positions along a gradient of environmental conditions, with different functional groups or guilds being differentially tolerant to variations in these conditions. Vegetation structure and plant habit seem to have a stronger influence on insectivores and some generalist frugivores/insectivores of understory (E-DI e V-FI), while plant composition plays a more important role for other specialist frugivore of canopy (C-FI, E-FI e C-LF) and probably for seed-eaters. Nectarivores showed high tolerance of these vegetation variables. We found a high spatial heterogeneity among habitats associated with differences in plant species composition. The habitats also had an asynchronous temporal pattern in fruit abundance and significant differences on monthly means of morphological and nutritional traits of fruits over vertical strata and among habitats. At the landscape level, these patterns suggest that, as a whole, the mosaic of different habitats can be seen as a non-seasonal unit, where the different patches complement each other in fruiting phenology. These conditions may affect bird communities because they were characterized by dynamic systems with temporal fluctuation in abundance and bird species composition. Significant correlation among fruit variables and bird abundance suggest that some bird species move into or out of habitats according to more favorable fruit availability. In general, birds eat a high diversity of fruit species; but at the same time, they show c1ear preferences and select fruits according to morphological and nutritional traits. The fruit morphological specialization may be associated with bird size, because the smaller birds had the smaller morphological niche breadth. In relation of morphological fruit selection, the larger birds selected fruits with larger seed mass and size and while the smaller birds selected fruits with small seeds mass and size. In contrast with the high morphological specialization found in most birds, the general pattern observed for nutritional traits is a generalist feeding strategy. It seems that the strong nutritional imbalance characterizing the pulp of most fruit species should force frugivores to adopt a mixed-species diet with high variation on nutritional content in order to get a balanced input of energy, protein, vitamins, and minerals. The bird species showed a wide flexibility concerning the nutritional fruit traits but not with the same nutritional requirement. The fruit species richness consumed by birds was not associated with bird size and neither with morphological and/or nutritional traits of fruit consumed

ASSUNTO(S)

nicho (ecologia) fenologia florestas - conservação ave

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