The complexity of the relations between the organisms and the environment are reflected through the energy content. So we tested the hypothesis on body energy content variation in invertebrates and its relation with some environmental factors (season, habitat type, trophic status and trophic guild). We expected higher energy values for phytophilous fauna, rainy season, in reservoirs with higher trophic levels and for herbivorous invertebrates. The results showed the influence of seasonality and trophic status of the reservoir on the energy content of invertebrates, which was higher in the rainy season and in the mesotrophic reservoirs, due to the input of allochthonous material during this season, confirming our initial prediction. A higher caloric content was recorded for carnivorous and detritivorous invertebrates. The differences between the trophic guilds were primarily related to the opportunistic feeding behavior, which may be considered as one of the main factors controlling the energy flow of benthic and phytophilous invertebrates.
IntroductionThe energy dynamics in aquatic ecosystems can be better understood by studying the caloric content of the organisms (MUNN and BRUSVEN, 1991). However, the small size of aquatic invertebrates is often a problem for obtaining energy measurements, mainly due to the difficulty of sampling a large number of small specimens needed for calorimeter measurements (FELLER and WARWICK, 1988;LUCAS, 1992). Several studies have improved the knowledge on the energy content of several organisms.Since the pioneer work of LINDEMAN`s (1942) about the energy availability and trophic chains, several research projects were carried out in aquatic marine and freshwater ecosystems of temperate regions. A study performed by WISSING and HASSLER (1971) in freshwater ecosystems showed that the caloric values of invertebrates were related to seasonal variations. For example, the energetic content of Chironomidae was higher in the summer, because this is the growing season and quickly declined in the winter. STANCZYKOWSKA and LAWACZ (1976) also recorded higher energy value of Dreissena polymorpha in summer. Several others studies have stressed the importance of energy measures for the understand- ing of the dynamics of aquatic ecosystems (GOLLEY, 1961;CUMMINS and WUYCHECK, 1971; DRIVER et al., 1974;SALONEN et al., 1976;CLARKE et al., 1985;DAUVIN and JONCOURT, 1989;BEUKEMA, 1997;DOYLE et al., 2007). Nevertheless, even in well-studied temperate regions, the knowledge of the caloric content is still incomplete for many organisms (DOYLE et al., 2007).In Neotropical aquatic ecosystems, few studies have thus far investigated the caloric content, so data on the energy content of organisms in these ecosystems is even more scarce and mostly restricted to ichthyofauna (NGAN et al., 1993;DORIA and ANDRIAN, 1997;BENEDITO-CECILIO et al., 2004;SANTANA et al., 2005;ESPÍNOLA et al., 2008), aquatic macrophytes (ESTEVES and THOMAZ, 1990;DOURADO et al., 2004;LOPES et al., 2006) and a few invertebrate group...