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The functioning of systems arranged in cascades of reservoirs can be explained by the Cascading Reservoir Continuum Concept, providing a theoretical framework for addressing ecological processes. In this context, this study tested the following hypotheses: (i) the benthic macroinvertebrate assemblage shows a nested distribution along a reservoir cascade; and (ii) local factors explain the structure of the benthic assemblage in every reservoir along the cascade. Macroinvertebrates play essential role in aquatic systems, especially due to recycling and, in reservoirs, as important links in every food chain. Sampling was conducted quarterly between October 2006 and September 2010 in six reservoirs located in the São Francisco River, Brazil. The benthic macroinvertebrate assemblage showed nested distribution in the reservoirs, indicating that a loss of species occurs along the cascade. Each reservoir presented a different set of variables that explained the distribution of macroinvertebrates, showing the importance of local factors determining the composition and distribution of benthic assemblages in the reservoirs. Therefore, there is a clear interaction between the position of a reservoir along a cascade and the macroinvertebrate assemblages, which indicate the importance of considering this pattern during the decision-making process of constructing new dams on rivers already regulated.

Climate change and species invasions interact in nature, disrupting biological communities. Based on this knowledge, we simultaneously assessed the effects of climate change on the native distribution of the Amazonian fish Colossoma macropomum as well as on its invasiveness across river basins of South America, using ecological niche modeling. We used six niche models within the ensemble forecast context to predict the geographical distribution of C. macropomum for the present time, 2050 and 2080. Given that this species has been continuously introduced into non-native South American basins by fish farming activities, we added the locations of C. macropomum farms into the modeling process to obtain a more realistic scenario of its invasive potential. Based on modelling outputs we mapped climate refuge areas at different times. Our results showed that a plenty of climatically suitable areas for the occurrence of C. macropomum occurrence are located outside the original basins at the present time and that its invasive potential is greatly amplified by fish farms. Simulations of future geographic ranges revealed drastic range contraction in the native region, implying concerns not only with respect to the species conservation but also from a socio-economic perspective since the species is a cornerstone of artisanal and commercial fisheries in the Amazon. Although the invasive potential is projected to decrease in the face of climate change, climate refugia will concentrate in Paraná River, Southeast Atlantic and East Atlantic basins, putting intense, negative pressures on the native fish fauna these regions. Our findings show that short and long-term management actions are required for: i) the conservation of natural stocks of C. macropomum in the Amazon, and ii) protecting native fish fauna in the climate refuges of the invaded regions.

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ABSTRACT. Fish diet studies contribute to understanding resource partitioning and community trophic structure. The present paper characterizes the diet of "peixe-cachorro" species Acestrorhynchus britskii and A. lacustris in Sobradinho reservoir, Bahia State, Brazil. Bimonthly samples (November 2006 to July 2008 were taken in the lotic, transition and lentic stretches of the reservoir, using gillnets overnight. A total of 899 A. britskii and 476 A. lacustris stomachs were analyzed, 70% of which were empty. Their content indicated the species are predominantly piscivorous, with 18 prey fish species identified. However, each prey occurred in a single month, except for Anchoviella vaillanti, recorded in 80% of months for A. bristski, and Tetragonopterus chalceus in 25% for A. lacustris. The species presented high food overlap (Cλ = 0.992), owing to the occurrence of Actinopterygii (bits) and Actinopterygii in all months. Regarding prey fish alone, a differentiated intake and lower food overlap was detected, in the flood (Cλ = 0.427) and drought (Cλ = 0.172) seasons, in the lotic (Cλ = 0.434), transition (Cλ = 0.089) and lentic (Cλ = 0) stretches, and in overall overlap (Cλ = 0.236). The spatial and seasonal differences in the intake of different prey fish by both species suggest an opportunistic feeding habit and a competition reduction mechanism for food resources.Keywords: natural feeding, peixe-cachorro, piscivory. RESUMO. Composição da dieta e sobreposição alimentar deAcestrorhynchus britskii e A. lacustris (Characiformes: Acestrorhynchidae) do reservatório de Sobradinho, rio São Francisco, Estado da Bahia. Estudos sobre a dieta de peixes contribuem para o entendimento da partilha de recursos e da estrutura trófica da comunidade. O presente trabalho caracteriza a dieta dos peixes-cachorro Acestrorhynchus britskii e A. lacustris no reservatório de Sobradinho, Estado da Bahia. Coletas bimestrais noturnas (Novembro/2006 a Julho/2008) foram efetuadas nos trechos lótico, transição e lêntico do reservatório, empregando redes de espera. Foram analisados 899 estômagos de A. britskii e 476 de A. lacustris, aproximadamente 70% dos quais se encontravam vazios. Seu conteúdo evidenciou tratar-se de espécies predominantemente piscívoras, com 18 peixes-presa identificados. Entretanto, cada presa ocorreu num único mês, exceto Anchoviella vaillanti, registrada em 80% dos meses para A. bristski e Tetragonopterus chalceus em 25% deles para A. lacustris. As espécies apresentaram elevada sobreposição alimentar (Cλ = 0,992), pela ocorrência de Actinopterygii (partes) e Actinopterygii não-identificado em todos os meses. Entretanto, considerando apenas os peixespresa, foi observado consumo diferenciado e menor sobreposição alimentar, nos períodos de cheia (Cλ = 0,427) e seca (Cλ = 0,172), nos trechos lótico (Cλ = 0,434), de transição (Cλ = 0,089) e lêntico (Cλ = 0), e na sobreposição geral (Cλ = 0,236). A diferença espacial e sazonal no consumo de peixes-presa distintos pelas duas espécies sugere hábito alimentar oportunista e mecanis...