Estrutura funcional de peixes amazônicos no contexto da mudança climática

Amazonian floodplains are dynamic systems whose ecological organization is shaped by seasonal hydrological variability. However, increasing concern has emerged regarding the destabilizing effects of increasingly frequent and intense extreme hydroclimatic events on the structure and functioning of fish assemblages in the Amazon. In this context, this thesis evaluated how seasonal (across hydrological periods) and interannual hydrological variability (1999–2023), as well as the recent occurrence of extreme hydroclimatic events, influence the structure, reorganization, and functional resilience of fish assemblages in a Central Amazon floodplain lake over two decades. In the first chapter, assemblage functional composition was assessed based on biomass-weighted functional traits, using relative biomass and community-weighted means (CWM) to investigate temporal responses to hydrological variability and extreme events. In the second chapter, functional alpha diversity metrics (FRic, FEve, and FDiv) and functional beta diversity components (total, turnover, and nestedness) were estimated to examine functional space occupancy and the mechanisms underlying assemblage reorganization. Additionally, functional trajectory analyses explicitly incorporated the temporal dimension of functional dynamics by synthesizing the magnitude, directionality, velocity, and coherence of functional changes throughout the historical time series. Generalized additive models (GAMs) were applied to evaluate temporal variation, effects of hydrological periods, and the influence of continuous hydrological descriptors, including relative anomalies in river water level and in the duration of hydrological periods. The results indicated that functional structure responded predominantly to continuous hydrological variability and hydrological anomalies, exhibiting gradual and, non-linear patterns over time that were more pronounced than average differences among seasonal periods. Functional composition varied mainly through gradual adjustments in trait dominance, with differentiated responses to environmental conditions and extreme events. Functional alpha diversity was especially sensitive to hydrological anomalies, particularly functional richness, whereas functional evenness and divergence reflected internal rearrangements within functional space associated with adjustments in the contribution of persistent traits. Functional beta diversity was dominated by the nestedness component, indicating gradual and hierarchical reorganizations throughout the time series. Functional trajectories revealed predominantly intra-annual changes associated with seasonal transitions, combined with high interannual variability. Although trajectories did not exhibit cumulative directionality, they showed temporary deviations associated with extreme hydroclimatic events, contrasting recurrent and reversible patterns with contingent responses to specific hydrological conditions. Overall, the results suggest the maintenance of a relatively consistent functional structure over time, interpreted as evidence of functional resilience in fish assemblages, sustained by continuous internal reorganizations and by the predominance of more generalist and functionally redundant traits. Nevertheless, the recurrence and intensification of extreme events indicate potential vulnerabilities that may promote the progressive erosion of less redundant traits, with implications for the functioning and stability of Amazonian floodplain ecosystems.