Relações tróficas entre três espécies sintópicas de Rivulus (Cyprinodontiformes: Rivulidae) em igarapés da Reserva Ducke, Manaus, Amazonas

Abstract

This study aimed to analyze the trophic relations between Rivulus micropus, R. obscurus and R. kirovskyi in temporary ponds in the Reserva Florestal Adolpho Ducke, Amazonas, Brazil. Sampling was conducted between February and June 2013. A total of 149 specimens of R. micropus, 210 of R. kirovskyi and 23 of R. obscurus were captured. Diet was assessed using the stomach’s degree of filling (DF), relative volume (V%) and Frequency of Occurrence (FO%) of food items, that were used for the calculation of the Feeding Index (FIi). The feeding strategies were presented separately by species and according to the condition of sintopy. Analyses of trophic niche breadth were carried out at the individual and species level (Levins’ index), and dietary overlap (Morisita-Horn’s index) was calculated between two pairs of species: R. micropus with R. kirovskyi; and R. kirovskyi with R. obscurus. The three species were classified as invertivorous. The food spectrum of R. micropus included 25 items, represented mainly by Hymenoptera. The diet of R. kirovskyi was represented by 22 items, with a predominance of autochthonous resources, especially chironomid larvae, and the niche breadth of the species was narrow. Rivulus obscurus presented 13 food items comprised by both autochthonous and allochthonous resources, mainly nymphs of Hemiptera and Hymenoptera; its niche breadth was wider when compared to the other two species, but showed inter-individual variation with some individuals showing narrower trophic niche. There was a very low dietary overlap between pairs of species under syntopic occurrence when compared to the diet of individuals in a single-species condition in the ponds, which may indicate therefore competition and niche displacement. The three species used the most abundant food resources in the ponds, but showed some degree of feeding selectivity, especially in relation to the origin of the items (autochthonous or allochthonous). The ingestion of prey does not seem to be determined only by the abundance or availability in the environment, but perhaps by its energy content, which would be in agreement to the optimal foraging theory.