The Amazon rainforest has experienced rapid land-use changes over the last few decades, including extensive deforestation that can affect riparian habitats and streams. The aim of this study was to assess responses of stream fish assemblages to deforestation and land cover change in the eastern Amazon. We expected that percentage of forest in the catchment is correlated with local habitat complexity, which in turn determines fish assemblage composition and structure. We sampled 71 streams in areas with different land uses and tested for relationships between stream fish assemblages and local habitat and landscape variables while controlling for the effect of inter site distance. Fish assemblage composition and structure were correlated with forest coverage, but local habitat variables explained more of the variation in both assemblage composition and structure than landscape variables.Inter site distance contributed to variance explained by local habitat and landscape variables, and the percentage of variance explained by the unique contribution of local habitat was approximately equivalent to the shared variance explained by all three factors in the model. In these streams of the eastern Amazon, fish assemblages were most strongly influenced by features of instream and riparian habitats, yet indirect effects of deforestation on fish assemblage composition and structure were observed even though intact riparian zones were present at most sites. Long-term monitoring of the hydrographic basin, instream habitat and aquatic fauna is needed to test for potential legacy effects and time lags, as well as assess species responses to continuing deforestation and land-use changes in the Amazon. Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for PROCAD/ CAPES funding (project no 88881.068425/2014-01), the graduate scholarship for TOB and senior internship scholarship for LFAM to conduct research at Texas A&M University (process 88881.119097/2016-1). The manuscript was improved during the review process by addressing the thoughtful comments from Philip Kaufmann and an anonymous reviewer.

The aims of the study were to identify differences in alpha and beta diversity of Odonata larvae of the suborders Zygoptera and Anisoptera found between continuous forest sites (forest) and oil palm sites with forested buffers (oil palm), and to evaluate the extent of turnover and nestedness of communities within each habitat type. Twenty‐nine streams were sampled, 11 in forests and 18 in oil palm sites in the eastern Amazon. Alpha diversity of Zygoptera and Anisoptera was higher in streams at oil palm sites. Variation in species composition measured by beta diversity is primarily structured by turnover. Biotic heterogeneity of Zygoptera was higher in oil palm sites, while no difference was found in Anisoptera. Forested streams had more wood in the streambed, whereas oil palm sites had finer sediment, higher non‐agricultural human impact, water temperature, and road proximity index. Anisoptera turnover was positively correlated with water temperature and amount of wood in the streambed; Zygoptera turnover was positively correlated with non‐agricultural human impact. The patterns observed in Zygoptera can be attributed to the presence of forested buffers, which may have influenced the selection of foraging sites by adults and determined larval distribution. We conclude that oil palm plantations can change the environmental structure of streams and influence genus richness and turnover in Amazon streams. These results might help explain changes caused by oil palm plantations on Anisoptera and Zygoptera assemblages.

Considering the increasing importance of analysing spatial structure in ecological studies, the aims of the present study were to test whether fluvial distances and environmental factors are important drivers of the β-diversity of stream fish assemblages, and whether β-diversity is different in distinct hydrological periods. Specimens were sampled at 33 stream sites in the eastern Amazon. Eight environmental variables were measured at each site and fluvial distances between pairs of stream sites were determined. Environmental variables were the main factors structuring fish assemblages in both periods. However, fluvial distances were important only during the flood period. This can be related to the formation of extensive flood plains in this period, which increases connectivity between streams, breaking habitat isolation and increasing the regional signal for fish species. The higher correlation of β-diversity with environmental variables during the flood period may be related to decreased dispersal limitations and intermediate dispersal. Finally, β-diversity was higher during the flood period, highlighting the importance of the heterogeneity of the flood plain to stream biota. The results of the present study indicate that spatial and environmental factors play complementary roles in structuring fish assemblages in Amazon streams, and that β-diversity was affected by changes in the habitat connectivity experienced in different hydrological periods.

Studies of trait–environment relationships provide important tools for the prediction of the response of biological communities to environmental alterations. The Amazon basin presents enormous potential for the development of research on this type of relationship, given the diversity of both its fish fauna and the aquatic ecosystems this fauna inhabits. The present study investigated the association between local environmental variables and the functional traits of fish in 54 streams of six major Amazonian basins. We identified the relationship between the characteristics of the streams (channel morphology, channel habitat units, riparian vegetation cover, large woody fragments and instream cover for aquatic organisms) and fish traits related to locomotion, habitat use and feeding behaviour. The fish fauna of the broader, deeper and more slowly flowing streams was dominated by nektobenthic species that exploit autochthonous resources such as fish and invertebrates. In narrow, fast‐flowing streams, by contrast, there was a predominance of benthic fishes with varying feeding habits, including periphytivorous and invertivorous species. Narrow, shady streams were inhabited by nektonic species adapted for the exploitation of resources from the marginal vegetation. The results of this study contribute to the understanding of the association between the functional structure of fish assemblages and local environmental variables in Amazonian streams. We hope that these findings will stimulate further research into the natural variation in stream fish assemblages that will ensure the development of more effective management strategies that better protect these important aquatic ecosystems.

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Environmental filtering and dispersal limitation are essential processes affecting the variability of ecological communities. However, their relative contributions are highly debated and remain largely unknown in several systems, such as the hyperdiverse Amazon Basin. We determined the relative role of local, catchment, spatial, and biogeographical variables on the taxonomic and functional alpha and beta diversity of stream fish. We sampled 54 streams across six river basins in the Amazon. For each stream, we obtained 35 local habitat variables and 11 climate-catchment variables. Watercourse distances and basin identity were converted into spatial and biogeographical variables, respectively. We found that taxonomic alpha diversity responds both to spatial and local predictors, whereas its functional counterpart was mainly associated with local variables. Biogeography was the main factor structuring taxonomic and functional beta diversity, with a secondary contribution of catchment and local variables. Locally, substrate type and isolation determined the number and relative abundance of species and traits. The shared variation between biogeographical and environmental variables, especially altitude and slope, were strongly associated with beta diversity patterns, indicating a joint role of habitat filtering and dispersal limitation. Our results show the need to include both spatial and environmental variables in studies of stream communities at large spatial scales, as they are related to distinct processes that regulate community structure. We also encourage future studies to account for the responses of multiple facets of biodiversity to different drivers, as they provide essential and complementary information for community ecology and biogeography.

Drainage basins are inherently hierarchical and are composed of a series of nested subsystems, in which the functions and structure of lower levels depend on the features of higher levels. For a comprehensive understanding of the functioning of river systems, it is necessary to identify which factors are important at different scales and how they interact. Considering the importance of assessing lotic systems in the Amazon, our aim was to answer the following question: how do regional features at catchment scale constrain local physical habitat of streams? We sampled 55 streams distributed among six protected river basins of the Amazon, examining the associations of 11 catchment metrics with 146 local variables describing physical habitat structure derived from field measurements. Multivariate analyses showed that basins were structured according to different factors at both scales; variables related to substrate, cover for aquatic organisms and fast channel habitats were explained by altitude, catchment slope and proportion of coarse fragments in soils. Altitude was the most important catchment variable, strongly affecting flow velocity and regulating channel morphology and sediment transport. Spatial differences in environmental heterogeneity indicate that different processes act at each scale; this emphasizes how difficult it is to choose the most relevant spatial scale in ecological studies. Our results highlight the importance of regional variables, especially altitude and slope, as drivers of local‐scale environmental heterogeneity. We hope these results will help in developing more efficient monitoring projects and restoration practices to better understand and conserve aquatic resources in the Amazon Basin. Copyright © 2017 John Wiley & Sons, Ltd.