Conexões tróficas e avaliação da sazonalidade na estrutura da ictiofauna associada a bancos de macrófitas no Baixo São Francisco

• Ano de defesa: 2019
• Autor(a) principal: Silva, Milena Gonçalves da
• Orientador(a): Brito, Marcelo Fulgêncio Guedes de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Programa de Pós-Graduação: Pós-Graduação em Ecologia e Conservação
• Palavras-chave em Português: Habitat (Ecologia); Conservação do meio ambiente; Cadeias alimentares (Ecologia); Plantas aquáticas; Nicho (Ecologia); Teia trófica; Itens alimentares; Sobreposição de nicho; Guildas tróficas
• Palavras-chave em Inglês: Food web; Food items; Niche overlap; Trophic guilds
• Link de acesso: http://ri.ufs.br/jspui/handle/riufs/11882

Macrophytes are used as reproductive sites, foraging areas, refuge from predators and nursery for juveniles and small species, then they represent an important habitat for ichthyofauna. In addition, they provide a larger area for food resources due to the availability of prey substrates and represent one of the most important biotic factors for structuring fish communities. This study aimed to analyze space-time the trophic structure of the fish community associated with macrophyte banks in an anthropized section of the Lower São Francisco under the influence of the Xingó Hydroelectric Plant. Standardized bimonthly samplings (April/2015 to March/2016) were held in four locations using four drag strokes (10 m long, 5 mm mesh) close to the banks with aquatic macrophytes in the afternoon to collect fish. The specimens collected were anesthetized with eugenol, fixed (formalin 10%) and preserved (alcohol 70%). In the laboratory, five specimens of each species per sampling point and period were selected for biometrics and analysis of stomach contents, in which food items were identified and quantified volumetrically. In data analysis, the richness and diversity of items consumed was calculated, using the Simpson's Diversity Index to characterize the food spectrum at each point and sample period. The volumetric proportion of items consumed in each of the taxonomic categories was obtained by checking whether there is a difference between the points and periods through the ANOSIN Similarity Analysis (two-way), once the dissimilarities were visualized by NMDS and the items responsible for the variation identified in SIMPER. The proportion of allochthonous and autochthonous items, the Food Index (IAi%) of the items consumed by each species and trophic guilds were also calculated according to the similarity in the species' diet from a cluster analysis using the unweighted average of a matrix Euclidean Distance. The sharing of food resources was obtained according to the calculation of food overlaps and bipartite food webs were built for two link thresholds (LT = 0.00 and 0.05). Most of the fish collected and analyzed were small characiforms including the abundant and frequent Hemigrammus marginatus, H. brevis, Astyanax fasciatus e Phenacogaster franciscoensis. Another highlight was the presence of large carnivorous juveniles (Serrasalmus brandtii, Crenicichla sp., Cichlasoma sanctifranciscense, Astyanax lacustris e Hoplias malabaricus) who resort to macrophytes in search of food and fed on the most abundant fish families. Most of the food items found were of autochthonou origin, corroborating the macrophytes importance as a source of resources for the fish community in this environment. This is related to the homogenization of the points studied by the removal of marginal vegetation that negatively influences the contribution of allochthonous resources. Different dietary patterns were observed for abundant species from variations in foraging strategies, with H. brevis and P. franciscoensis feeding directed to surface items and H. marginatus to the bottom. The specie A. fasciatus did not present spatial segregation in the food and presented an omnivorous and opportunistic diet due to its higher allochthonous consumption. Among the built guilds (algivores, invertivores, insectivores and omnivores), algivores had more prominence in the overlays mainly involving invasive species (Oreochromis niloticus e Metynnis lippincottianus) with native ones. The resources segregation was verified among the analyzed species, indicating that the resources are limiting and the species tend to compartmentalize their niches and avoid competitive exclusion. The least impacted points (3 and 4) showed greater species richness and, consequently, larger and more complex webs, as in the rainy season. From the results obtained, it was found that the hypotheses that affirm greater connectivity and density of connections in the trophic webs of the rainy season and in points 3 and 4 were corroborated.