Padrões de diversidade beta de assembleias de peixes em ribeirões submetidos a diferentes graus de conservação

Abstract

Through the estimation and analysis of the β diversity (differences in species composition between habitats), it is possible to identify and relate the processes operating at multiple spatial and temporal scales in the determination of the species distribution. Thus, this analytical approach proves its great importance for the understanding of the structural mechanisms of these communities, as well as providing support in recognizing and predicting the impact of anthropic influence on these ecosystems. The objective of this study was to evaluate the variation in the composition and diversity of fish assemblages (beta diversity) along streams subjected to different degrees of conservation (Tibagi river watershed, Paraná, Brazil). Through quarterly collections (March, June, September and December) were analyzed the information of the assemblages of fish and limnological parameters of the three watersheds that cross the municipality of Londrina (PR) in the northwest-southeast sense, toward the Tibagi river (Cambé, Cafezal and Taquara), during the year of 2013. Two models of β diversity were applied: β1 based on the average species richness and β2 calculated from the maximum richness. Two spatial scales were studied: in the collection stations and between the collection stations in each of the streams studied throughout the year of 2013. The patterns of β diversity found along the longitudinal gradient were different between the streams. The β1 index remained above the β2 during the year of 2013 in all the cases presented, indicating higher values of shared species and lower gains and losses of species (turnover) in the collections. Among the streams, the Taquara showed the greater heterogeneity in the structure of the assemblage along the longitudinal gradient, due to less intense changes expressed by the values of β1 and β2 over the space and the time, revealing itself more balanced in the point of view of the assemblage structure. The Cambé and Cafezal streams showed similar responses to environmental pressures, reflecting greater homogenization of the environmental parameters and the consequent high dominance of opportunistic species, which resulted in greater disruption of assemblages along the space-time gradient. It was possible to conclude that the three streams analyzed travel different extents within the city of Londrina, showing alterations in their physiognomic and limnological characteristics along their courses, which tend to promote variation in the structure of the fish assemblage.