Katharina Eichbaum Esteves

Composition and trophic structure of a fish community of a clear water Atlantic rainforest stream in southeastern Brazil

As part of a larger project that aimed to determine the factors that regulate fish productivity in a clear water river of the Atlantic rainforest, São Paulo State, Brazil, composition and the trophic structure of the fish community of the middle course of the river were studied from January 1995 to May 1996. Of the 17 species collected, Mimagoniates microlepis, Schizolecis guentheri, Phalloceros caudimaculatus and Kronichthys heylandi accounted for 83.2% of the total fish abundance. Most of the species were insectivorous (35.7%), followed by detritivores (21.4%), benthivores (14.2%), omnivores (14.2%), herbivores (7.1%), and piscivores (7.1%). Results of food overlap analysis as calculated by the Index of Morisita showed that 17.5% of the species pairs overlapped. Habitat segregation, however was observed among most of the species, suggesting some degree of food partitioning. Despite the characteristics of this escarpment river, which produces spates year round, no seasonal variation in diet was observed, suggesting that although food abundance may fluctuate throughout the year, most items are in constant supply. The importance of allochthonous food was considered and it appears that, though only a few species feed on this source (including detritivores), they make up 87.2% of the total fish abundance. The low abundance of most of the fishes, the high number of endemic species and the strong dependence of the species on a few food resources suggest that these systems are sensitive to anthropogenic impacts and require future studies.

Food partitioning among some characids of a small Brazilian floodplain lake from the Parana River basin

SynopsisResource partitioning and the seasonal patterns of food intake of four characids (Astyanax fasciatus, A. bimaculatus, A. schubarti and Cheirodon stenodon) were studied during 1988 in a floodplain lake of Mogi-Guaçú River, Sao Paulo State. For interspecific comparisons, data of the previously studied Moenkhausia intermedia have also been used. A. fasciatus and A. bimaculatus can be considered omnivorous species, while A. schubarti and C. stenodon are predominantly herbivorous. The river flood cycle (following the wet season October-March and dry season April-September) seems to influence both seasonal food intake and food overlap between species. February-March and September-October are probably the months of highest food availability, and the months preceding these periods have the lowest resource amount. Our study shows that both omnivorous and herbivorous species modified the intensity of their interactions according to this cycle. Omnivorous species maintained fairly segregated diets when resources were presumably limited, and showed a rapid change from distinct food niches in the dry season to widely overlapping ones when resources were presumably more abundant. Conversely, the herbivorous species showed higher overlap during the dry season. Acute cyclic changes in the environment, as observed in this study, suggest the necessity of small interval sampling in food partitioning studies in tropical freshwater floodplains, in order to understand how species interact and cope with changes in food availability.

Feeding ecology of three Astyanax species (Characidae, Tetragonopterinae) from a floodplain lake of Mogi-Guaçú River, Paraná River Basin, Brazil

SynopsisThe feeding ecology of three characids (A. fasciatus, A. bimaculatus and A. schubarti) was studied monthly during 1988 in Lake Inferñao, a major floodplain lake of the Mogi-Guaçú River in the State of São Paulo. River flooding directly influenced the diet of the omnivorous A. bimaculatus and A. fasciatus which responded to maximum inundation (March) by consuming predominantly allochthonous insects. In contrast, A. schubarti was less influenced by the river flood cycle on qualitative changes in diet and relied basically on aquatic macrophytes and periphytic algae. The importance of zooplankton in the diet of the three species was low, and may be attributed to its low density in the water column (< 1 ind l−1). Ontogenetic diet changes were evident for the three species. For A. fasciatus and A. bimaculatus the importance of zooplankton was high at the early stages, decreasing with size. A. schubarti at younger stages consumed diversified items which gradually decreased quantitatively up to the size class of 65 mm; from this size onwards, the diet became restricted to the consumption of periphytic algae and macrophytes.

Assessing the importance of the riparian zone for stream fish communities in a sugarcane dominated landscape (Piracicaba River Basin, Southeast Brazil)

In the Neotropics, the effect of agriculture on freshwater habitats is still poorly understood, particularly with respect to sugarcane expansion to meet increased ethanol demands. The variation in taxonomic composition, community attributes and trophic structure of fish assemblages from streams under different riparian zone preservation conditions were studied. Nine stream reaches under the following riparian vegetation conditions were selected: Native Forest (NF), with mostly primary forest; Secondary Forest (SF), which included sites with vegetation in an advanced stage of regeneration surrounded by sugarcane plantations; and Sugarcane sites (SC), located in areas without riparian vegetation, adjacent to sugarcane crops. Forty-one species were collected. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that community composition and trophic structure were significantly explained by riparian condition and spatial variations, while diversity, richness, abundance and biomass were only explained by season and space, with higher diversity and richness at the SF sites. Abundance-Biomass curves (ABC curves) suggested that sugarcane plantations destabilized fish assemblages, especially at the more intensively managed sites, which seem to influence stream integrity and associated fish fauna. We concluded that both physical conditions of streams and some attributes of fish communities reflected the different levels of preservation of the riparian buffers, but given the influence of regional processes which have a pervasive role in shaping local assemblages, land use at the watershed scale seemed to be important especially to explain the higher richness and diversity found at the SF sites.

Feeding ecology of a stream fish assemblage in an Atlantic Forest remnant (Serra do Japi, SP, Brazil)

This study aimed to characterize the trophic structure of the fish assemblage in streams of the Serra Japi, an ecotonal area between the Atlantic Forest and inland forests of Sao Paulo State, Southeastern Brazil. Fish were collected with electrofishing equipment in 15 sites covering different regions, substrate types and riparian vegetation, distributed throughout the Caguacu River, Caxambu, Pirai and Guapeva River micro-basins, during the rainy (January/February) and dry season (June) of 2007. The 589 specimens analyzed from 22 species, were assigned to different trophic groups, discriminated through a matrix of similarity, based on the food index (IAi). The results show the formation of seven groups with a predominance of insectivorous and omnivorous species, followed by detritivores, piscivores, omnivore-carnivores and herbivores, which consumed mostly items of autochthonous origin, where algae and young insects were dominant. Canonical correspondence analysis (CCA), correlating the biomass of trophic groups to environmental variables, showed that omnivores, insectivores and omnivore-carnivores displayed a wide distribution, while detritivores, herbivores and piscivores were restricted to specific locations, related to different physical and chemical variables as total nitrogen, conductivity and temperature. Despite the increase in total biomass at the most urbanized sites, the results indicate that the streams maintain a diverse community, suggesting that most of them are in preserved conditions.

Environmental factors associated with fish distribution in an urban neotropical river (Upper Tietê River Basin, São Paulo, Brazil)

The rivers and streams of the large urban centers in Southeast Brazil are increasingly being degraded, demanding expanded conservation efforts. This study was conducted in the Grande River, one of the main tributaries of the Billings Complex, a reservoir that is a strategic fresh water resource for the São Paulo metropolitan region. Water quality, habitat features and fish fauna were investigated at seven sites along the longitudinal gradient with the aim of identifying the distribution patterns and relative contributions of the environmental factors. The water samples and environmental characteristics were recorded, and fish were collected during the rainy (January to March) and dry seasons (July and August) of 2009. The water quality varied along the river, with higher values of conductivity, fecal coliforms and total phosphorus in the lower reach, indicating a strong influence of the urban area. Twenty-two fish species were recorded, two of which are considered endangered. A canonical correspondence analysis (CCA) indicated marked differences in species composition between the river’s upper and lower reaches, which was mainly attributed to vegetation cover and the presence of different meso-habitats, such as riffles and pools. Trychomycterus spp. and Astyanax paranae were associated with the upper reaches, while Astyanax fasciatus and Astyanax bockmanni, Cyphocharax modestus, Hoplias malabaricus and Hypostomus ancistroides occurred in the lower reaches. Despite the disturbance in water quality and riparian vegetation in the lower river section, no detectable changes in community structure were observed. However, the presence of some tolerant species, such as Astyanax fasciatus, Hoplosternum littorale and Hypostomus ancistroides, may indicate that the community is experiencing initial stages of disturbance.

Anuran Communities in Different Riparian Habitats: Native Forest, Secondary Forest, and Sugarcane

Abstract. This study aimed to test the influence of different riparian habitats on the structure of anuran communities in southeastern Brazil. Nine stream stretches were selected representing three different riparian habitat types: Native Forest, Secondary Forest, and Sugarcane. A total of 223 individuals of 17 species and five families were captured. The Chao1 richness index indicated that after standardizing the sampling effort the Native Forest sites had higher richness than the Secondary Forests and Sugarcane sites, which presented similar richness. The Abundance and Biomass Curves for the Native Forest sites showed an overlap of the weight and abundance curves, suggesting that these sites presented lower disturbance levels. A disturbance gradient from Native Forest towards Sugarcane sites was observed. The Bray-Curtis similarity index showed a significant effect of riparian condition on species composition. Our results suggest that Sugarcane and Secondary Forest sites limit the distribution of certain species, such as those from the family Hylidae species related to litterfall, and enable colonization by open-habitat species that are capable of resisting anthropic pressure.

The fish fauna of an Atlantic Forest conservation area in the largest urban center of South America (São Paulo, SP, Brazil) and its relationship to some environmental factors

This study describes the composition and distribution of fish species in an Atlantic Forest Environmental Protection Area located in the city of São Paulo (APA Capivari-Monos), with the aim of determining the composition, distribution and the relationship of the community to local environmental conditions. Three main rivers (Capivari, Taquacetuba and Embu-Guaçu) were sampled by electrofishing at a total of 10 sites. Twenty-five species were recorded, of which 20% (Characidium oiticicai, Pseudocorynopoma heterandria, Pseudotocinclus tietensis Trichomycterus paolence and Glandulocauda melanopleura) are considered endangered for the State of São Paulo. Community attributes varied between rivers and along the longitudinal axis, indicating that several species have a restricted distribution and specific ecological requirements. Este estudo descreve a composição e distribuição de espécies de peixes em uma Área de Proteção Ambiental de Mata Atlântica localizada na cidade de São Paulo (APA Capivari-Monos), com o objetivo de determinar a composição, distribuição e a relação da comunidade com características ambientais. Três rios principais (Capivari, Taquacetuba e Embu-Guaçu) foram amostrados com pesca elétrica em um total de dez pontos de coleta. Vinte e cinco espécies foram registradas, das quais 20% (Characidium oiticicai, Pseudocorynopoma heterandria, Pseudotocinclus tietensis, Trichomycterus paolence e Glandulocauda melanopleura) são consideradas ameaçadas para o Estado de São Paulo. Os atributos da comunidade variaram entre os rios e ao longo do eixo longitudinal, indicando que diversas espécies apresentam uma distribuição restrita e exigências ecológicas específicas.