Oil palm plantations have expanded around the world, increasing concern about its pressure on deforestation rates and the homogenization of the landscape. In this context, the present study aimed to evaluate the impact of oil palm plantations on the physical characteristics of streams in Amazonia and their effects on Heteroptera, Odonata and Fish assemblages. A total of 23 streams were sampled, eight within fragments of primary forest, while 15 were in oil palm plantations. Data were collected on characteristics of the channel morphology, substrate, hydraulics, instream cover for aquatic organisms, riparian vegetation, human impacts and woody debris. Instream cover and proximity of human impacts were the variables that had the greatest effects on the physical structure of the streams, showing variation between streams of forest in pristine areas and oil palm plantations. Of the analyzed parameters, substrate, instream cover and woody debris influence the richness of Heteroptera, Odonata and Fish. The impact of oil palm plantations on local streams depended on the size of the plantations, and they cannot be considered an adequate substitute for lost habitats in efforts to preserve the physical habitat of Amazonian streams. Any type of conversion of the natural forest can have direct or indirect impacts on the dynamics and structure of these environments, with potentially negative consequences for their biodiversity. The maintenance of an adequate buffer zone of native riparian vegetation adjacent to the streams that flow through the plantations recommended, because this appears to be the principal factor determining the physical conditions of these streams.
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.
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