RESUMO

Interactions between terrestrial and aquatic systems influence the structure of river habitats and, consequently, affect their benthic macroinvertebrate composition. The aim of this study was to evaluate the effects of spatial and environmental variables (local physical and chemical variables of water and regional landscape characteristics) on the benthic macroinvertebrate community of the Pandeiros River Basin. Biotic and abiotic variables were evaluated at 20 sampling sites distributed across the primary sub-basins of the Pandeiros River Basin. We found that the macroinvertebrates were primarily affected by environmental variables. The most important environmental variables were pebble proportion and water conductivity at the local scale (7.2% of explained variation) and elevation and nonforest areas at the regional scale (6.9% of explained variation). The spatial variables were representative only in shared explained variation with the environmental matrices (local-spatial = 0.2% and regional-spatial = 2%; all matrices combined = 4.4%). Sampling sites with higher non-forest areas, lower elevations, and steeper slopes presented low pebble fractions and higher electrical conductivities. Habitat diversity was lower when the percentage of pebbles decreased, resulting in decreased taxonomic richness and diversity in macroinvertebrate communities. High electrical conductivities and non-forest areas also had negative effects on macroinvertebrate density due to the loss of habitat diversity. We conclude that higher proportions of pebbles in the substrate and higher altitudes were likely the primary variables for positive effects on the taxonomic richness and density of macroinvertebrate communities.

Assuntos

RESUMO

Interactions between terrestrial and aquatic systems influence the structure of river habitats and, consequently, affect their benthic macroinvertebrate composition. The aim of this study was to evaluate the effects of spatial and environmental variables (local physical and chemical variables of water and regional landscape characteristics) on the benthic macroinvertebrate community of the Pandeiros River Basin. Biotic and abiotic variables were evaluated at 20 sampling sites distributed across the primary sub-basins of the Pandeiros River Basin. We found that the macroinvertebrates were primarily affected by environmental variables. The most important environmental variables were pebble proportion and water conductivity at the local scale (7.2% of explained variation) and elevation and nonforest areas at the regional scale (6.9% of explained variation). The spatial variables were representative only in shared explained variation with the environmental matrices (local-spatial = 0.2% and regional-spatial = 2%; all matrices combined = 4.4%). Sampling sites with higher non-forest areas, lower elevations, and steeper slopes presented low pebble fractions and higher electrical conductivities. Habitat diversity was lower when the percentage of pebbles decreased, resulting in decreased taxonomic richness and diversity in macroinvertebrate communities. High electrical conductivities and non-forest areas also had negative effects on macroinvertebrate density due to the loss of habitat diversity. We conclude that higher proportions of pebbles in the substrate and higher altitudes were likely the primary variables for positive effects on the taxonomic richness and density of macroinvertebrate communities.(AU)

Assuntos

RESUMO

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambaí, Ivaí and Paraná rivers and in the Itaipu Reservoir (upper Paraná River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambaí River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivaí River also differed from the Paraná River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambaí River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivaí River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds. (AU)

O objetivo deste trabalho foi avaliar o papel de fatores abióticos na ocorrência de larvas de peixes. As amostragens foram realizadas mensalmente em 12 estações (agrupadas em 4 áreas) nos rios Amambaí, Ivaí e Paraná e no reservatório de Itaipu, de outubro de 1994 a janeiro de 1995 (época de desova). Simultaneamente, foram obtidos dados de temperatura, pH, condutividade elétrica, oxigênio dissolvido, nível da água, velocidade da água e precipitação. Análises de Componentes Principais (PCA) e de Correspondência com Remoção do Efeito de Arco (DCA) foram aplicadas para sumarizar os dados abióticos e as densidades de larvas, respectivamente. O rio Amambaí diferiu significativamente das outras áreas em relação aos fatores abióticos. O reservatório de Itaipu diferiu significativamente das outras áreas quanto à composição de espécies, tendo o rio Ivaí também diferido do rio Paraná neste aspecto. A relação entre os eixos da PCA e DCA foi significativa, indicando que os fatores abióticos influenciam as larvas. Por exemplo, Leporinus elongatus preferiu o rio Amambaí, Hypophthalmus edentatus, Plagioscion squamosissimus e Hoplias aff. malabaricus o reservatório de Itaipu e Pimelodus maculatus, Auchenipterus osteomystax e Iheringichthys labrosus o rio Ivaí. Assim, sugerimos que cada espécie seleciona um conjunto de características abióticas em um dado ambiente utilizado como local de desova. (AU)

Assuntos

RESUMO

The purpose of this study was to evaluate the role of abiotic factors on fish larvae occurrence. Samplings were carried out monthly at 12 stations (grouped in four areas) in the Amambaí, Ivaí and Paraná rivers and in the Itaipu Reservoir (upper Paraná River basin), from October 1994 to January 1995 (spawning season). Simultaneously, we obtained water temperature, pH, electrical conductivity, dissolved oxygen, water level, water velocity, and rainfall. Principal Component Analyses (PCA) and Detrended Correspondence Analyses (DCA) were applied to summarize abiotic and larvae density data, respectively. Amambaí River differed significantly from the other areas in relation to abiotic factors. Itaipu Reservoir differed significantly from the other areas considering species composition, and the Ivaí River also differed from the Paraná River. The relationship among PCA and DCA axes were significant, indicating that abiotic factors do influence larva. For example: Leporinus elongatus prefered the Amambaí River, Hypophthalmus edentatus, Plagioscion squamosissimus, and Hoplias aff. malabaricus the Itaipu Reservoir, and Pimelodus maculatus, Auchenipterus osteomystax and Iheringichthys labrosus the Ivaí River. We suggest that species selected some abiotic factors characteristic to a given environment as spawning grounds.

O objetivo deste trabalho foi avaliar o papel de fatores abióticos na ocorrência de larvas de peixes. As amostragens foram realizadas mensalmente em 12 estações (agrupadas em 4 áreas) nos rios Amambaí, Ivaí e Paraná e no reservatório de Itaipu, de outubro de 1994 a janeiro de 1995 (época de desova). Simultaneamente, foram obtidos dados de temperatura, pH, condutividade elétrica, oxigênio dissolvido, nível da água, velocidade da água e precipitação. Análises de Componentes Principais (PCA) e de Correspondência com Remoção do Efeito de Arco (DCA) foram aplicadas para sumarizar os dados abióticos e as densidades de larvas, respectivamente. O rio Amambaí diferiu significativamente das outras áreas em relação aos fatores abióticos. O reservatório de Itaipu diferiu significativamente das outras áreas quanto à composição de espécies, tendo o rio Ivaí também diferido do rio Paraná neste aspecto. A relação entre os eixos da PCA e DCA foi significativa, indicando que os fatores abióticos influenciam as larvas. Por exemplo, Leporinus elongatus preferiu o rio Amambaí, Hypophthalmus edentatus, Plagioscion squamosissimus e Hoplias aff. malabaricus o reservatório de Itaipu e Pimelodus maculatus, Auchenipterus osteomystax e Iheringichthys labrosus o rio Ivaí. Assim, sugerimos que cada espécie seleciona um conjunto de características abióticas em um dado ambiente utilizado como local de desova.

Assuntos