| Summary: | In historical and geologic times significant climatic and topographical changes have taken place, the topographical changes are those where it varies the coordinate «z» that corresponds to the altitude or depth of the environment. The climatic changes can produce topographical changes, and in the other hand, topographical changes more rarely produce climatic changes. The human action generates many of these changes and it accelerates them notably. The dynamic interaction in the time of the three factors, climatic, topographical, and human it is what is denominated «environmental change». Inside this mark the dispersion of Hypostomus commersoni is analyzed in the east of the pampasia, from 1957 until the present time. New records for Crenicichla lepidota and of some species introduced recently: Ictalurus cf. punctatctus, Acipenser cf. baerii and Oreochromis sp., are given. Great part of the climatic change perhaps is modelable and predictable, but the topographical changes and the human factor have a high grade of randomness, for what the goods of the environmental change are, for the time being, impredecibles.
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