The trophic niche of two sympatric Aegla Leach species (Crustacea, Aeglidae) in a tributary of hydrographic basin of Pelotas River, Rio Grande do Sul Brazil

Freshwater anomurans of the Aeglidae are restricted to tropical and temperate South America. Some of the more than 60 known species are sympatric, among them Aegla camargoi (Buckup & Rossi, 1977) and Aegla leptodactyla (Buckup & Rossi, 1977), occur in the mountainous region of Rio Grande do Sul, the southernmost Brazilian state. The interactions between these two sympatric species, especially sharing of food resources, is still largely unknown; this is the reason this study was done. Samples of each species were collected at 6 and 12 hour intervals during spring, summer, autumn and winter. The degree of fullness of their stomachs was calculated by the point method, frequency of occurrence of different types of food debris and feeding index. The breadth of the niche was estimated for each species using Levins' Index and the niche overlap with Pianka's and Schoener's methods. Both species fed principally on macrophytes and immature insects of Ephemeroptera, Trichoptera, Coleoptera and Diptera. They feed anytime of the day with no seasonal differences. Although the breadth of the trophic niche of each species showed small seasonal variations, the trophic niches of the two species overlapped during all seasons. These results suggest that these species are generalist omnivores and share food resources available in the environment.

Coexistent species; Decapoda; diet; niche overlap