Diversidade funcional e taxonômica de Chironomidae em reservatórios do semiárido em um cenário de seca extrema

Abstract

Current climate change has revealed a greater frequency of extreme weather events. Extreme drought is an example of an extreme climate, which causes severe fluctuations in the water volume of aquatic ecosystems. This has put pressure on species to adapt to new conditions. However, not all species manage to persist under the new climate regimes, which can compromise the local biodiversity. Therefore, this dissertation sought to evaluate how extreme drought events, affected the water volume of reservoirs from different basins in the semiarid and how this variation affected the coexistence of Chironomidae assemblies. We tested the hypothesis, the extreme drought scenario will condition the local diversity, favoring the occurrence of genres with functional traits able to tolerate the hydric stress, caused by water volume fluctuations. Also, the taxonomic and functional diversity, particularly its β component, will decrease due to the biotic homogenization of the Chironomidae assemblies in both basins. To test the hypothesis, the Chironomidae from six reservoirs of different regions of the Brazilian semiarid were studied, (256 points) in 2014, 2015, and 2019. Period of extreme drought, with precipitation only from 2018, but below the annual average. The Chironomidae assemblies were then analyzed in different components of the α, β, and  diversity, in the taxonomic dimension using Simpson’s index and functional dimension the Rao’s index. To evaluate change in the assemblies as a function of water volume, the taxonomic and functional richness, Simpson Diversity, Rao Quadratic Entropy, functional redundancy, and the dominant functional traits of the assemblies were calculated, (community weighted means- CWM). The main results showed that the taxonomic and functional β-diversity was proportionally higher than α-diversity in the Paraíba basin, except in 2019 (similar α and β proportions). In the Piranhas-Açu basin, the reverse occurred, except in 2015 (only lowed β-functional). The indexes of diversity and the CWM results showed that fluctuations in water volume exert influence on the taxonomic composition and functional answer of assemblies, being more evident for the Piranhas-Açu basin. The combined effect of fluctuations in water volume and habitat conditions act as a filter, limiting the coexistence of genres and functions. Promoting different answers depending on the characteristics of the basin/reservoirs, such as a moderate turnover of species and functions or only turnover species, but similar function also in the situation of greater drought and lower water volume, or even biotic homogenization in periods of greater volume.