CONICET | Buscador de Institutos y Recursos Humanos

The habitat preferences, temporal dynamics in density and the life history of two species of mayflies, Metamonius anceps andMeridialaris chiloeensis, were investigated in a Patagonian mountain stream over a period of one year. Benthic samples weretaken in a low order Nothofagus forested stream. M. anceps was univoltine with small nymphs predominating in winter andemergence occurring in summer. M. chiloeensis showed a bivoltine life cycle with a winter and summer generation, andemergence period in spring and summer. Both species were significantly more abundant in the low water period than in the highdischarge season. Gravels supported significantly more individuals of M. chiloeensis than sand in pools and leaf packs. Temporaloverlap of abundance between species was low. The existence of different life history strategies and the temporal shift of maingenerations and density peaks were critical to allow species coexistence.Keywords: insects, Ephemeroptera, life cycle, ecology, river, habitat preference

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