Present trends in river studies

Resum

A review of recent studies on river ecology is presented. Emphasis is laid on the importance of basin processes which are key factors in defining the structure and function of river communities. At present rivers are viewed as parts of ecosystems where disturbance and spatial heterogeneity play a central role. Biotic interactions (predation, competition) do not seem to be important at the ecosystem level because of the frequency and intensity of disturbances in the rivers. In sorne of them, however (the lower part of the largest rivers), or during short periods of time, herbivores and predators (especially fish) may have great involvement in the production and structure of the cornmunity. On the other hand, much recent work has been done in the temperate zone, and sorne of the more recent ideas may well have to be re-examined in the future, when more comprehensive studies of small streams in tropical areas become available. The lack of knowledge about Mediterranean rivers is also emphasized. Many of the recent ideas in river ecology have emerged in discussions at meetings. Those of the North American Benthological Society and the Regulated Rivers Symposia deserve special mention as forums for the exchange of fruitful ideas. Finally, tribute is paid to Prof. Margalef for his pioneer studies on river ecology and his always stimulating and iconoclastic ideas on the general rules of science.