Combined effects of climate change and deforestation have altered precipitation patterns in the Amazon. This has led to changes in the frequency of extreme events of flood and drought in recent decades and in the magnitude of the annual flood pulse, a phenomenon that influences virtually all aspects of river-floodplain ecosystem dynamics. Analysis of long-term data revealed abrupt and synchronous changes in hydrology and fish assemblage structure of a floodplain lake near the confluence of Amazon and Negro rivers. After an intense drought in 2005, the assemblage assumed a different and fairly persistent taxonomic composition and functional structure. Declines in abundance after 2005 were more pronounced for species of all sizes having equilibrium life history strategy, large species with periodic life history strategy, and for all trophic levels except primary consumers. Our results suggest that the extreme drought triggered changes in the fish assemblage and subsequent anomalous hydrological conditions have hampered assemblage recovery. These findings stress the need to account for climatic-driven hydrological changes in conservation efforts addressing aquatic biodiversity and fishery resources in the central Amazon.

The present study analyzed and compared the daily consumption of foods of animal origin in eleven communities of the Lower Amazon, Trombetas and Purus Rivers, representing three different management systems and levels of conservation in the Brazilian Amazon. All food items of animal origin were weighed by at least 10% of the families in the study communities during a week in each period of the flood cycle between 2006 and 2008. Fish was the most important food, and was consumed during six days of the week, with an average rate of 169 kg.person -1 .year -1 . Game was second in importance, with 37 kg.person -1 . year -1 . This yearly rate of fish consumption is one of the highest in the world and is almost double the minimum recommended by the World Health Organization. The dietary patterns reflect both the isolation of the communities from large urban centers and the better preservation of the local environments due to the existence of protected areas. Environmental degradation may thus have effects on the health and food security of local populations. The study emphasizes the need for the implementation of public policies and participative management initiatives.

We analyzed the stomach contents of 116 individuals belonging to seven fishes species in order to investigate seasonal changes in feeding strategy and how trophic interactions between species affect community structure in an Atlantic rainforest stream in Southeastern Brazil. Oligosarcus hepsetus and Pimelodus sp. consumed fewer items during the winter. Phalloceros caudimaculatus switched feeding habits from detritus during summer to algae during winter. These examples are related to variations in food availability and species feeding selectivity. The highest diet overlap values, for most species, as measured using Schoener's index, were observed in summer, along with a species tendency to be more generalist. Feeding pattern variation may influence the fish community structure.Key words: Atlantic rainforest, diet overlap, feeding variability, specialist, generalist. RESUMO

At broad scales in the Amazon, it is often hypothesized that species distributions are limited by geographical barriers, such as large rivers (river-barrier hypothesis). This hypothesis has been used to explain the spatial-distribution limits of species and to indicate endemism areas for several phylogenetic lineages. We tested the ability of the river-barrier hypothesis to explain patterns of species diversity and spatial-distribution limits for 1952 easily-detected species in 14 taxonomic groups that occur around the Madeira River, and our results indicate that the hypothesis that the Madeira River is the border between endemism areas and explains much of the diversity found in the region is inappropriate for >99% of species. This indicates that alternative hypotheses should be proposed to explain the limits of distributions of species around the Madeira River, as well as a revision of the criteria that are used to determine species-endemism areas.

Aim Evaluating how groups of organisms vary in dispersal capability and how environmental, spatial and temporal signals vary across multiple scales is critical to elucidating metacommunity theory. We examined whether the relative contributions of environmental, spatial and hydrological factors have different effects on organismal groups with different dispersal abilities at three spatial scales, and how this knowledge contributes to our understanding of metacommunity dynamics. Location Four major Brazilian floodplains, with the largest distance among them of 2,300 Km. Taxon 10 aquatic organismal groups, ranging from bacterioplankton to fish. Methods We sampled lakes connected to the main river in the low‐ and high‐water periods of each floodplain between 2011 and 2012. Different biological groups were analysed across three hierarchical spatial scales (fine, intermediate and subcontinental) within and between floodplain systems. We applied a series of partial redundancy analyses to estimate the relative contributions of environmental factors, spatial factors and hydrological period for each biological group. Results At the fine spatial scale, predominantly environmental factors and hydrological period structure metacommunities, although less so for microorganisms than for micro‐invertebrates and macro‐organisms. The relative importance of environmental factors increased at the intermediate spatial scale. At the subcontinental scale, the relative importance of spatial factors increased for all biological groups, but environmental factors remained the primary regulators of microorganisms even at the largest scale. Main conclusions This study design allowed us to make more robust inferences about the mechanisms responsible for regulating community structure of distinct biological groups at different spatial scales. Our results suggest that biological groups displaying distinct body size likely determine the spatial extent at which environmental, spatial and hydrological processes prevail as the primary regulators of community structure. These findings are important in guiding the conservation and management of floodplain biodiversity because these systems are naturally highly heterogeneous in space and time.