Padrões de espacialidade no uso dos recursos alimentares pela ictiofauna de dois riachos neotropicais com diferentes aspectos de preservação.

Abstract

This study aimed to analyze the longitudinal pattern on the trophic organization, in order to infer the environmental quality of two streams with distinct characteristics, a rural stream and an urban stream. Bothe streams are of fist order and are located in Maringá, PR, Pirapó river sub-basin. The fish samples were taken bimonthly between July/2007 and June/2008, at three sites (head, middle-region and mouth) in each stream. 5016 individuals were captured, belonging to five orders, seven families and 15 species, which were added in the upstream-downstream direction, regardless of the stream. In rural stream the most consumed feeding resources were mainly aquatics and terrestrial invertebrates, as well as plants and detritus, exploited in a balanced manner along the longitudinal profile. It is noteworthy, however, a marked spatial change in the aquatic invertebrates composition, showing a larger diversity of food-organisms. In urban stream, the main exploited resources were aquatic invertebrates and detritus, being the taxonomic composition uniform, highlighting in the stomachs contents, Chironomidae and Oligochaeta (indicators of poor environmental quality) in the entire length of the stream, indicating that the macrofauna is less diverse and more homogeneous. The niche breadth values (Levins' index) were, in general, low along both streams and no significant differences were detected between the stretches of the same stream and not even between the two streams. The most of the species' pairs presented low values of feeding overlap (Pianka's index) and the fishes were organized into trophic groups (grouping analysis, Euclidian distance), showing that the fishes trophically segregate themselves. The results found in this study suggest that the rural stream still show conservation characteristics. Although not all types of testing has been extensive enough to detect such a feature, the ichthyofauna diet, for itself, had the expected range and was efficient to infer about the quality of the streams, if we consider that change in aquatic invertebrate taxa and the constancy of terrestrial invertebrates in fish diet constitute important factors for environmental assessment.