O papel de mudanças hidrológicas de ordem sazonal e climática na estrutura da assembleia e história de vida de peixes na confluência dos rios Negro e Amazonas

Abstract

Flow varability in space and time is widely regarded as a master variable that shapes the ecological characteristics of rivers and streams. Recently combined effects of climate change and deforestation have changed precipitation patterns in the Amazon, which in turn have changed the magnitude and timing of annual flow cycle. Effects of these changes on freshwater ecology and biology are poorly known. Here we investigated the effect of seasonal and interannual hydrological dinamics on assemblage structure and fish reproductive investment, emphasising the role of extreme events. Analysis of long-term data for hydrology and fish surveys in a floodplain lake near the confluence of Amazon and Negro rivers reveals that: i) seasonal connectivity with two large rivers plays important role on seasonal species turnover and populational recolonization. Temporal � diversity was high in the lake and the assemblage was dominated by seasonally transient species. Relatively large species known to feed on resources within the floodplain were captured almost exclusively during the flood period. During the dry season, the assemblage was dominated by fishes adapted to harsh conditions of high temperature and low dissolved oxygen concentrations; ii) analysis of long-term data set showed a significant and concordant changes in hydrology and assemblage structure. Major shifts coincided with an intense drought in 2005, followed by years with annual flood pulses of higher magnitude and earlier dry season onset. After 2005, the fish assemblage assumed alternative and persistent taxonomic and functional compositions indicative of a regime shift in response to an external driver; iii) the analysis of effects of annual hydrological condition on reproduction shows that extreme events and the interaction of extreme events and body condition affected female fecundity negatively. Females of Acestrorhynchus falcirostris, a piscivorous species, reduced the fecundity when had poor body condition in year of intense flood. Advanced, long and intense dry seasons had negative effect on Psetrogaster rutiloides fecundity and interacted with body condition on Triportheus angulatus fecundity. Mean oocyte size was more affected by environmental condition, as high population density and hydrological situation and its interaction with phenotype than only by individual’s phenotype (body size and body condition). Population density had a positive effect on the mean oocyte size in all studied species. The combination of these results suggests that biodiversity conservation and inland fisheries management in the Amazon will need to account for recent climatic and hydrologic changes that have the potential to induce ecological regime shifts and population dynamics.