Abstract Patterns of beta diversity of plankton communities in rivers have been mainly determined by hydrological factors that alter the dispersion and composition of species and traits. Rotifers in the Guamá River (eastern Amazonian River) were sampled (monthly between October 2017 and June 2019) to analyze the temporal variation of taxonomic and functional beta diversity and its partitions (turnover and nestedness) as well as the effects of temporal, environmental, and seasonal dissimilarities. Taxonomic turnover and functional nestedness over time were observed as well as functional homogenization, which was arguably due to the hypereutrophic condition of the river. There were no seasonal differences in taxonomic and functional beta diversity probably due the low environmental dissimilarity. This study demonstrated that this Guamá River stretch presented low environmental dissimilarity and hypereutrophic waters, which benefited the establishment of a community of species with high taxonomic turnover over time, but with low functional dissimilarity and loss of some functions related to the functional traits evaluated in the ecosystem. It is important to point out that temporal studies should evaluate both taxonomic and functional aspects of communities, mainly because the effect of environmental changes may be more noticeable at the functional level of communities.

El manejo del régimen de inundación ha cambiado de manera significativa la dinámica natural de las inundaciones, que son responsables de la estructura y dinámica de las comunidades acuáticas en sistemas río-planicie de inundación. En este sentido, investigamos cómo la estructura de las comunidades zooplanctónicas responde a variaciones estacionales e interanuales en los sistemas de llanura de inundación, y los factores biológicos asociados con la abundancia de especies de las comunidades zooplanctonicas. Elaboramos también, un marco conceptual que describe los principales factores ecológicos asociados con la estructura de las comunidades para los sistemas del Alto río Paraná. Para ello se realizaron muestreos cada seis meses (potamophase en marzo y en septiembre limnophase) para caracterizar las variaciones intra e interanuales en la estructura de la comunidad entre 2000 y 2008. Las diferencias estacionales de la riqueza de especies, abundancia, índice de diversidad de Shannon y equitatividad, se llevaron a cabo utilizando procedimientos Bayesianos para mostrar predicciones probabilísticas de los datos ajustados para las principales fuentes variación. Análisis de ordenamiento no-métrico multi-dimensional (NDMS); procedimientos de permutación de respuestas múltiples (MRPP) y análisis de especies indicadoras (IndVal) fueron utilizados para evaluar y clasificar la estacionalidad de la estructura de la comunidad. Durante aguas altas (potamofase), la conectividad hidrológica favoreció el intercambio y dispersión de las especies en algunas lagunas, incrementando la diversidad local; durante aguas bajas (limnofase), la alta productividad local favoreció los táxones oportunistas, incrementando las especies dominante y disminuyendo la diversidad local. La disponibilidad de recursos alimenticios y la densidad de pequeños peces fueron los factores biológicos asociados con la dinámica estacional de la comunidad zooplanctonica; los cuales dependen de la fase hidrosedimentológica (potamofase o limnofase). Modificaciones del régimen hidrológico y limnológico relacionados con el manejo de inundación han promovido el reemplazo y empobrecimiento de la biota acuática, en las lagunas sin conexión afectadas, enfatizando así la importancia ecológica de la dinámica natural de inundaciones, que presenta pulsos regulares de inundación. El modelo conceptual que se presenta abarca desde interacciones entre diversas variables ambientales hasta mecanismos más comprensibles de las principales fuentes de variación de la comunidad.

Water flow management has significantly changed the natural dynamic of floods, which are responsible for the structure and dynamic of aquatic communities in river-floodplain systems. With the aim to elaborate a conceptual framework that describes the main ecological factors associated with zooplankton community structure in the Upper Paraná River, we investigated the mechanisms that regulate the communities structure and their response to inter-annual and hydro-sedimentological variations in the floodplain and the biological factors associated with species abundance in those communities. For this we conducted samplings every six months (potamophase in March and limnophase in September) to characterize intra and inter-annual variations in community structure between 2000 and 2008. The intra-annual differences on the species richness, abundance, Shannon diversity index, and evenness, were conducted using Bayesian procedures to show probabilistic predictions of the data fit to main variation sources. Non-metric multi-dimensional scaling (NMDS), multi-response permutation procedure (MRPP), and indicator species analysis (IndVal) were run to assess and characterize the seasonality of the community structure. During high water (potamophase), hydrologic connectivity favoured exchange and dispersal of species in some lakes, increasing local diversity; during low water (limnophase), higher local productivity favoured opportunistic taxa, increasing species dominance and decreasing local diversity. Food resources and density of small-size fish were biological factors associated with the seasonal dynamic of the zooplankton community; these factors were dependent on hydrosedimentological phase (potamophase or limnophase). Water levels and limnological modifications related to water flow management have promoted replacement and impoverishment of aquatic biota in affected lakes and have indicated the ecological importance of a natural dynamic flood, which displays regular flood pulses. The conceptual model presented encompassed interactions between diverse environmental variables to more understandable mechanisms of the main sources of community variation.

Ambientes temporários sofrem secas periódicas devido à escassez de água que interrompe a conectividade hidrológica com sistemas aquáticos adjacentes. No entanto, alguns ambientes retem água por mais tempo permitindo uma maior persistência das comunidades. Este estudo avaliou diferenças nas assembleias de microcrustáceos e na variabilidade limnológica entre poças perenes e temporárias em um rio intermimente na região semiárida da Bahia. As características abióticas das poças temporárias (temperatura da água, pH, alcalinidade total, condutividade elétrica e profundidade) foram mais afetadas do que nas poças perenes devido à perda total do volume de água. Isso pode ter contribuído para maior riqueza e índice de diversidade médio de microcrustáceos em alguns ambientes intermitentes, e a diferenças encontradas na estrutura das assembleias. Menores valores de diversidade e riqueza de espécies foram registrados nos locais com fatores físicos e químicos restritivos que tornaram o ambiente impróprio para os organismos, tais como: maior quantidade de sólidos em suspensão e condutividade elétrica da água e amplitude de variação do pH. Estes resultados sugerem que nos ambientes intermitentes, o desenvolvimento da comunidade é interrompido pela estação seca. Quando a água retorna, devido às chuvas ou soerguimento do lençol freático, cada ambiente apresenta um processo diferente de colonização. Nestas circunstâncias, a importância biológica dos ambientes aquáticos temporários é destacada, já que esses locais fornecem abrigos e têm um papel importante na manutenção da diversidade regional de ambientes aquáticos.

Temporary wetlands undergo recurrent drought due to the scarcity of water, which disrupts the hydrological connectivity with adjacent aquatic systems. However, some environments retain water for longer periods, allowing greater persistence of the community. The current study evaluated differences in the microcrustacean assemblages and limnological variability between perennial and intermittent pools in a semi-arid region of Brazil. The abiotic features (water temperature, pH, total alkalinity, electrical conductivity and depth) of intermittent pools were affected more than perennial pools due to loss of water volume. This may have contributed to a higher average richness and diversity index in some intermittent pools and differences in the structure of the assemblages. The lowest species richness and diversity were recorded where physical factors, such as a large quantity of suspended solids and variability in the electrical conductivity of the water and pH, make the environment unsuitable for these organisms. These results suggest that community development in intermittent pools is interrupted by the dry season; when the water returns, due to rainfall or rising groundwater, each pond undergoes a different process of colonization. In these circumstances, the biological importance of temporary aquatic environments is clear, since such pools provide shelters and have an important role in the maintenance of the regional diversity of aquatic environments.