In this paper we evaluate the importance of the environment and interspecific relationships in the pattern of organization of semiaquatic insect species in a mining area in the Eastern Amazon. For this, we used the characteristics (traits) of the species, considering abundance and sexual dimorphism, and amount of riparian vegetation in each stream. With this, we tested the following hypotheses: (a) the environmental impact caused by mining activity decreases the availability of resources in the streams and, therefore, species tend to be more different from each other (morphological divergence), to avoid competitive exclusion; (b) the presence of a larger portion of riparian vegetation in some streams modifies the organization of the semiaquatic insect assembly, so that species better utilize the resources of the environment. We sampled 16 streams in the municipality of Paragominas, in the Capim River Basin, in the state of Pará. We measured the physicochemical variables and the amount of riparian vegetation. No action of environmental filters was found for the total assembly, but we found significant morphological divergence for all analyzed traits. On the other hand, the separation of the streams into treatments with different portions of riparian vegetation showed that there are significant differences between them, regarding the pattern of species distribution. The treatment with the largest portion of forest (with 60% or more riparian vegetation), within 500m, has the species distributed over a larger area, indicating that these streams have greater availability of resources or that the species can use these resources more efficiently. Thus, it is possible to verify that the interspecific interactions in the assembly of semi-aquatic insects is shaping the way the local community is organized. In addition, the riparian vegetation in these streams is also an important factor in determining the organization of species.
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