Navegando por Assunto "Comunidade (Ecologia)"

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Acesso aberto (Open Access)
A comunidade ictica e suas interrelacões tróficas como indicadores de integridade biológica na área de influencia do projeto hidrelétrico Belo Monte-Rio Xingu, PA
(Universidade Federal do Pará, 2004-04) CAMARGO-ZORRO, Mauricio; ISAAC, Victoria Judith; http://lattes.cnpq.br/3696530797888724
This study presents applied methodologies to better understand the dynamics of mechanisms characterizing a portion of the Xingu River, with respect to fish communities living in that environment. Through the study of the ichthyofauna it is aimed to verify various environmental standard patterns, in order to assess the current conservation state of a part of the Xingu River. Based on surveys of the local ichthyofauna conducted over seasonal variations, analyses were conducted at the specieS, population and trophic guild levels. With regards to the ecological population level, study of biological parameters such as individual growth rates, asymptotic body length, mortality rates and size at first maturity were good indicators for a better understanding of the life history of those fish groups. Therefore a trend was observed in which species of relatively small body size to followed a "r" type strategy, whilw species of larger body sizes would follow the "k" strategy tactics. From a functional point of view, it was verified that guild community structure is not only a good indicator of convergence patterns to similar ecosystems as like the Xingu River studied stretch, but also a tool to assess its conservation status. A steady- state ecosystem model for the medium Xingu River sector indicated that it is a system highly instable, and simultaneusly look like a mature seasonal system. An apparent seasonal restriction of food availability observed in the studied river section could imply optimum use efficiency and transfer of the trophic resources. A biogeographic study was undertaken based on species occurrence in order to conceptualise the River stretch comprised between the confluences of the Iriri and Xingu Rivers up to the vicinity of of the village Senador José Porfirio, in the Xingu basin. By means of this analysis, it was possible to demonstrate that the medium upstream of waterfalls) and lower (downstream) courses of the Xingu River are parts of two endemic areas. The low affinity of species composition observed in these two sectors is attributed to geographic variations in the landscape. Therefore, the boundaries of the waterfalls around the village of Belomonte and the influence of the Amazon River in the lower Xingu course could trigger differences in ichthyofaunal composition and species abundance when compared to the medium course of that river. Finally, the importance of maintaining all hydrologic connectivity is pointed out in order to maintan the unity of the system, from the headwaters to the mouth. Impacts on environmental processes and fish populations in the medium course of the Xingu River as a result of the eventual construction of the Belemonte hydroelectric dam are discussed.
Acesso aberto (Open Access)
Ecologia de lagos da planície inundada do baixo Tapajós: diversidade, estrutura de comunidade de peixes e percepções socieconômicas dos moradores de Alter do Chão, Santarém-PA
(Universidade Federal do Pará, 2005-10-07) COSTA, Luiz Rodolfo Ferreira da; BARTHEM, Ronaldo Borges; http://lattes.cnpq.br/4192105831997326
Acesso aberto (Open Access)
Variação sazonal e espacial da estrutura de comunidades dos peixes demersais da Região de Foz dos Rios Amazonas e Tocantins - PA (0º 10'S - 2º30'N; 47º50'W - 50º30'W) - Brasil
(Universidade Federal do Pará, 1999-11-23) TORRES, Marcelo Ferreira; BARTHEM, Ronaldo Borges; http://lattes.cnpq.br/4192105831997326
The composition, abundance and frequency of the demersal fish fauna from the Amazon estuary were studied in three areas which ones were defined as circumscribed within the isobath ranges of 5-10 m, 10-20 m and 20-50 m. The main objectives of this work were to compare the diversity, abundance and distribution of demersal fish fauna in these three areas during one hydrological cycle, and evaluate the infiuence of environmental variables on the community structure. Samples were taken on board of two piramutaba fishing vessels, using a bottom trawl net, for a given seasonal survey of six 15-day trips in the dry season (March and Apri1/97) and in the rainy season (August and September/97). A number of 91 species were caught in a total of 237 samples and Sciaenidae and Ariidae were the most diverse families, represented by 25% of total species. The Ariidae' species which ocurred in the area were very abundant. The most abundant species were Macrodon ancylodon (Sciaenidae) (56,2%) and Brachyplatystoma vaillantii (Pimelodidae) (13,6%) in the rainy season, and Macrodon ancylodon (31%) and Stellifer rastrifer (15,8%) (Sciaenidae) in the dry season. In area 1 Brachyplatystoma vaillantli (Pimelodidae) and Macrodon ancylodon (Sciaenidae) were the most abundant species in both periods, and the same occurred for Macrodon ancylodon and Stellifèr rastrifer (Sciaenidae) in area 2, and for Macrodon ancylodon (Sciaenidae) and Bagre bagre (Ariidae) in area 3. The most frequent species sampled were Macrodon ancylodon (Sciaenidae) (40,9%) and Anchoa spinifer (Engraulididae) (35%) in the rainy season, and Macrodon ancylodon (Sciaenidae) (45,6%) and Anus grandicassis (Ariidae) (38,4%) in the dry season. In area 1 Brachyplatystoma vaillantii and Brachyplatystoma flavicans (Pimelodidae) were the most frequent species, considering each period; the same was observed for Macrodon ancylodon (Sciaenidae) and Bagre bagre (Ariidae) in area 2, and Macrodon ancylodon (Sciaenidae) and Anchoa spinifér (Engraulididae), in area 3. The dominant species were: Macrodon ancylodon (Sciaenidae) in the rainy season (56% of the specimens collected); and Macrodon ancylodon, Stellifér rastrifer (Sciaenidae) and Anus quadriscutis (Ariidae) in dry season, which represented 61% of fishes caught. In area 1, Brachypiatystoma vaillantii (Pimelodidae) and Macrodon ancylodon (Sciaenidae), were dominant (73%) in the rainy season, and both of them together with Anus grandicassis (Ariidae) were dominant (53%) in the dry season. area 2 only Adacrodon ancylodon (Sciaenidae) was dominant (64%) in the rainy season, and Macrodon ancylodon and Stellifer rastrifèr (Sciaenidae) were dominant (53%) in the dry season. In area 3, just one species Macrodon ancylodon (Sciaenidae) was considered dominant (70% in the rainy season and 49% in the dry season). Distribution patterns were influenced by salinity. Area 1 presented the greatest diversity and evenness as compared with the others. Area 2 presented the greatest richness, and area 3 presented the highest dominance. Three communities were identified: one characterized by species from continental waters that explore shallow areas at depths of less than 20 m; another one formed by salinity resistant species, distributed through a wide range from the estuary, mostly in the area circumscribed within the isobath range of 10-20 m; and a third one with marine species distributed in areas at depths of 10 m to 50 m.