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

Abstract

Resource 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 MogiGuacu 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 .

Aspectos da história natural de Astyanax scabripinnis Jenyns (Teleostei, Characidae) em um riacho de floresta com araucária no sul do Brasil

“…Estudos realizados com A. scabripinnis indicam a preferên-cia da espécie por rios de menor porte (CASTRO & CASATTI 1997, LEMES & GARUTTI 2002, CASATTI 2002, SHIBATTA et al 2002, VEREGUE & ORSI 2003, BENNEMANN et al 2005, onde os indivíduos consomem uma grande quantidade de recursos alóctones (SHIBATTA et al 2002, BENNEMANN et al 2005. Este fato parece estar diretamente relacionado com a capacidade de muitas espécies do gê-nero Astyanax em colonizar diferentes habitats (ESTEVES & GALETTI 1995, HAHN et al 1998, VILELLA et al 2002, ORSI et al 2004.…”

Preliminary data on the feeding habits of the freshwater stingrays Potamotrygon falkneri and Potamotrygon motoro (Potamotrygonidae) from the Upper Paraná River basin, Brazil

“…The biovolume corresponds to the area occupied by each food item in relation to the totality of ingested items, determined by the analysis of the stomach content on a milimetric plate (adapted from Esteves & Galetti Jr. 1995). The relative volume was determined through the displacement of a water column, using a graduated test tube.…”

“…The use of a volumetric method in the fish diet analyses through the measurement of the displacement in a graduate test tube is difficult when the items possess small size or are present in small amounts (Hyslop 1980). In these cases, the biovolume, defined as the area occupied by each food type (Esteves & Galetti Jr. 1995), can be used as an indirect measure of volume. In the present study, the advantage of the biovolume method was reinforced through the comparison between the values of the relative index of importance, calculated with the biovolume and the relative volume values.…”

Ritmicidade da alimentação e dieta de Metynnis roosevelti Eigenmann (Characidae, Myleinae) da Lagoa do Jiqui, Parnamirim, Rio Grande do Norte, Brasil

“…KEY WORDS. Metynnis roosevelti, fish , feeding rhythms, Jiqui Lake Através de estudos de cronologia alimentar em peixes, obtém-se informações valiosas quanto a aspectos práticos relativos à metodologia de análise de conteúdo estomacal, assim como de aspectos teóricos referentes a interações intra e interespecíficas (ESTEVES & GALETTI 1994, 1995 .Trabalhos sobre ritmos em peixes são realizados comumente no campo abordando-se três aspectos: (1) variação diária nas características populacionais através de inferências sobre a composição dos peixes capturados em redes de espera em vários intervalos do dia, (2) padrões alimentares através da inferência sobre o conteúdo do estômago em diferentes momentos do dia e 3) observação direta dos movimentos e alimentação através da utili zação de técnicas de mergulho (RUSAK 1981).Estudos sobre a organização temporal do padrão alimentar em peixes neotropicais de águas interiores, apresentam muitas possibilidades aplicáveis tanto para espécies isoladas , ou pares de espécies, quanto para conjuntos de peixes de um dado …”

“…KEY WORDS. Metynnis roosevelti, fish , feeding rhythms, Jiqui Lake Através de estudos de cronologia alimentar em peixes, obtém-se informações valiosas quanto a aspectos práticos relativos à metodologia de análise de conteúdo estomacal, assim como de aspectos teóricos referentes a interações intra e interespecíficas (ESTEVES & GALETTI 1994, 1995 .…”