Abstract
The changes imposed by dams on hydrological regime, water transparence and nutrient concentrations downstream affect biodiversity in relation to species richness and specific composition of the community. The aim of this work was evaluate this effect on periphyton, comparing richness and composition of periphytic algae in the Garças Lake, Upper Paraná River floodplain, between the years 1994, before construction of the Porto Primavera Reservoir, and after its operation in 2004. This floodplain lake showed an increase in species, from 113 in 1994 to 159 in 2004. A few species, however, were common during the last year, dominated by Zygnemaphyceae and some Bacillariophyceae species. The increase in algal diversity in 2004 may be the result of the ability of the system to adapt to environmental changes. However, the large change in the periphyton species composition suggests further impacts on the food web, demanding continuity of long-term studies in order to determine their consequences on the biodiversity as a whole.
Highlights
The relationship between diversity of an ecological community and its stability is not clear, and has been the subject of numerous debates and considerable research (Pielou, 1983; Colinvaux, 1986; Odum, 1989; Lampert and Sommer, 1997; Townsend et al, 2006)
The importance of the term stability has led to the use of different meanings
The Upper Paraná River floodplain is located between Porto Primavera Dam and Itaipu Reservoir, extending about 230 km (Agostinho et al, 2008)
Summary
The relationship between diversity of an ecological community and its stability is not clear, and has been the subject of numerous debates and considerable research (Pielou, 1983; Colinvaux, 1986; Odum, 1989; Lampert and Sommer, 1997; Townsend et al, 2006). For Pielou (1983), stability is the tendency of the community composition to remain constant. Colinvaux (1986) relates stability to ecosystem resilience (the ability of the system to, under stress, return to its original state when the stress is removed), and considers an ecosystem “stable” when the probability of species extinction is low. “Stability” may be defined as the persistence of the system structure (i.e., an ecosystem, community, or organism) over time, the ability of populations to withstand disturbances without marked changes in composition, and the tendency to remain in, or return to, a stable state (Glossário, 1997).
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