The influence of environmental factors on the seasonal dynamics and composition of Rotifera in the Sapucaí River arm of Furnas Reservoir, MG, Brazil. Biota Neotrop. 10(4): http://www.biotaneotropica.org.br/v10n4/en/ abstract?article+bn03510042010.Abstract: Seasonal fluctuations in the dynamics of the plankton rotifer populations in an oligo-mesotrophic branch of a tropical reservoir were analyzed with respect to the possible influence of environmental conditions (physical, chemical and biological), with emphasis on biological interactions. Samples were taken monthly from August 2006 to July 2007. The well-defined climatic seasons were reflected in variations of the physical and chemical properties of the water. The zooplankton community consisted mainly of Rotifera, Cladocera and Copepoda, with occasional representatives of Chaoborus brasiliensis (Diptera), Ostracoda, Protozoa and Turbellaria. Rotifera was the dominant group in zooplankton community in 5 of the 12 months of the study and were represented by 35 taxa. Redundancy analysis between the rotifer population abundances and the set of environmental variables showed significant (p < 0.05) positive correlations with the chlorophyll a in the rainy season. In the dry period, predation was probably the environmental factor that had the strongest effect on rotifer populations; in particular, the density of the cyclopoid Thermocyclops decipiens showed significant (p < 0.05) negative correlations with many of the rotifer population abundances. In addition, analysis of the co-occurrence of different rotifer species indicated strong competitive interactions between populations, during the rainy period (p < 0.001). Among the biotic environmental factors analyzed, algal biomass had an important role during the rainy period and interrotifer competition was also significant in these months. It was probably that predation by the cyclopoid copepod Thermocyclops decipiens determined the structure and dynamics of the rotifer populations in the Sapucaí arm of the Furnas reservoir, during the dry period. Resumo: Mudanças na dinâmica sazonal dos rotíferos planctônicos em uma porção oligo-mesotrófica de um reservatório tropical foram avaliadas em relação às variáveis ambientais (físicas, químicas e biológicas). As coletas foram realizadas mensalmente de agosto de 2006 a julho de 2007. As estações climáticas foram bem definidas, refletindo em variações nas características físicas e químicas da água. A comunidade zooplanctônica foi representada pelos grupos: Rotifera, Cladocera, Copepoda, e ocasionalmente por Chaoborus brasiliensis (Diptera), Ostracoda, Protozoa e Turbellaria. Os Rotifera foram dominantes na comunidade em cinco dos 12 meses amostrados, tendo sido representados por 35 taxa. A análise de redundância entre as densidades das populações de Rotifera e as diversas variáveis ambientais indicou correlação positiva significativa (p < 0.05) com a concentração de clorofila a no período chuvoso. No período seco, provavelmente a predação foi o fator ambiental que mais influe...