A traíra Hoplias aff. malabaricus (Bloch, 1794) na planície de inundação do alto rio Paraná : influência sobre as assembléias de peixes e aspectos da auto-ecologia.
This study tested experimentally the hypothesis that traíra Hoplias aff. malabaricus is a keystone predator in isolated lagoons of the upper Paraná River floodplain. The experiment was conducted from April to October 2002, through an initial manipulation of traíra density (levels of treatment: addition, removal and reference). Treatment effects were evaluated on descriptors of fish assemblage structure (species richness, abundance, equitability and biomass), through repeated measures analysis of variance, in two habitat categories (open and macrophyte-dominated areas). In spite of being recorded in all assemblages and depended on habitat category, reductions in species richness were significantly more pronounced in lagoons where H. aff. malabaricus was removed. In these lagoons, the number of individuals was also significantly lower than in those where the piscivore was added or maintained in natural densities. Equitability showed opposite tendencies. Analysis of relative abundance by size-classes revealed a sharp reduction in the number of small-sized individuals (< 3cm), contributing to the absence of pronounced alterations in biomass. These evidences supported our hypothesis and demonstrated that the understanding of mechanisms by which predators affect the persistence of prey species constitutes a challenge for future researches, especially in tropical ecosystems, in which phytoplankton changes in Paraná River were verified, in function of the formation of Porto Primavera Reservoir and the climatic alterations that occurred during the period studied (1993-1994 and 2000-2005), especially those related to El Niño and La Niña phenomena. In the second chapter entitled "Interannual variation of phytoplankton in a river-flooding lake system (Upper Paraná River, Brazil)", we verified that the alterations of phytoplankton structure in Patos Lagoon and Ivinhema and Paraná rivers were associated to the fluctuations of hydrosedimentological regime of Ivinhema and Paraná rivers, probably, influenced by the phases La Niña (2000-2001) and El Niño (2003-2004) Southern Oscillation cycle (ENSO).
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| Format: | Thesis/Dissertation biblioteca |
| Language: | Portuguese |
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Universidade Estadual de Maringá. Departamento de Biologia. Programa de Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais.
2005
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| Subjects: | Temperature, Consumption, Growth, Empirical modelling, Size, Keystone, Neotropical fishes, Predation, Whole-lake experiment, Modelagem empírica, Crescimento, Temperatura, Tamanho, Floodplain, Assemblage structure, Hoplias aff. malabaricus, Planície de inundação, Peixes neotropicais, Espécie-chave, Experimento em lagoas, Estrutura da assembléia, Consumo, Predação, Ciências Ambientais, |
| Online Access: | http://hdl.handle.net/1834/10159 |
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