Padrões alimentares durante um período de seca e investigação de endozoocoria por Podocnemis expansa (TESTUDINES: PODOCNEMIDIDAE) na Reserva Biológica do Rio Trombetas, PA, Brasil

Abstract

Understanding how organisms get their energy from the environment represents an important tool for management and conservation of species in a biological community. Turtles are a major biodiversity component in the ecosystems they inhabit, assuming different feeding strategies among species. Podocnemis expansa is a widely distributed aquatic chelonian species throughout large rivers and associated lakes in the Amazon. These animals inhabit an extensive diversity of habitats, and they are considered to assume an herbivorous diet by known literature. Because they ingest a large volume of fruits and seeds from threes in várzea and igapó wetlands, Podocnemis expansa take great potential to act as seed dispersers in nature. Thus, this work aimed to investigate feeding patterns in a P. expansa population in the Rio Trombetas Biological Reserve during a dry period, by analyzing size and sex effects on diet. Furthermore, this work aimed to investigate the possibility of P. expansa as endozoochorous agents during the rainy season. Linear regressions were performed in order to examine whether individuals sizes define the volume of animal and plant material consumed. Sexual differences in feeding were investigated by MANOVA, in which the two former ordination axes generated from a NMDS analysis on the volume of each food category ingested were used as dependent variables. Besides, we calculated simplified Morisita indexes to assign similarities among males, females and juveniles diets, as well as the indexes of relative importance for each food category. We analyzed the stomach contents of 48 P. expansa individuals, six of which were males, 25 were females and 17 were juveniles. We found no relationship between animals sizes and the volume of animal material ingested (R² = 0.008928; p = 0.239), neither between animals sizes and the volume of plant material ingested (R² = 0.01451; p = 0.5698). Leaves were the most important food category for males, females and juveniles. For the period, P. expansa supply did not vary by gender (F1,46 = 1.0033; p = 0.4101). However, males ingested significantly more sediment than females and juveniles. Although the dry season features as an essential period for reproduction, the results indicate that feeding during the dry season makes wispy contributions to P. expansa growth. During the rainy season, we performed germination tests on the seeds extracted from the feces of 18 P. expansa. Seven of the 18 animals captured defecated morphological intact seeds, which were taken to a germination experiment under wet vermiculite. In number of 14, the seeds belonged to the taxa Pouteria elegans (Sapotaceae), Psidium sp. (Myrtaceae), Oryza sp. (Poaceae), Duroia sp. (Rubiaceae) and to other four non-identified morphotypes. None of the seeds showed signs of germination, therefore it’s not possible to assert that P. expansa act as seed dispersers. The low number of extracted seeds, however, is not statistically conclusive to put away the role of these turtles in seeds dispersal. Thus, the presented data serve as an important tool for future experiments on the investigation of endozoochory by P. expansa, mainly by indicating plant species – highlighting Duroia sp. – that keep morphological integrity after passing through the digestive tracts of these animals.