Despite their high morphological similarity, sibling species often coexist in aquatic habitats presenting a challenge in the framework of niche differentiation theory and coexistence mechanisms. Here Brachionus calyciorus species complex inhabiting Lake Tingtang, a shallow eutrophic lake, was used to gain insights into the mechanisms involved in coexistence in sibling species. The animals were collected once a week from Lake Tingtang in July 2011, when the water temperature increased from 28℃ to 32℃. Then the animals were clonally cultured in lab, and their COI genes were sequenced and analyzed to reconstruct the coexistence dynamics of sibling species. Forty-seven rotifer clones from four collections and two sibling species were used to calculate their life table demographic parameters including life expectancy at hatching, average lifespan, generation time, net reproduction rate, intrinsic rate of population increase and the proportion of sexual offspring at 28℃ and 32℃, and with 1.0×10⁶, 3.0×10⁶ and 5.0×10⁶ cells/ml of Scenedesmus obliquus as their food, and the responses in the life table demographic parameters to water temperature, algal density and collection batch were analyzed to explore the coexistence mechanisms. In total of 59 samples, 38 haplotypes were defined, among which 2 distinct lineages (Lineages Ⅰ and Ⅱ) were revealed by phylogenetic analysis. Sequence divergence was 13.9%-15.6% between the two lineages, indicating the occurrence of two sibling species (sibling species T1 and sibling species T2). The relative abundance of sibling species T1 in the density of the species complex decreased rapidly from the first collection to the third collection; and in the fourth collection, the sibling species disappeared from the water body. However, the relative abundance of sibling species T2 increased from the first collection to the fourth collection; and after a week, the sibling species also disappeared from the water body. All the life table demographic parameters of sibling species T1, and the generation time, the net reproduction rate, the intrinsic rate of population increase and the proportion of sexual offspring of sibling species T2 significantly varied with increasing collection data. In the first, second and third collection, the average lifespan, the life expectancy at hatching and the generation time of sibling species T1 were markedly longer than those of sibling T2. In the second collection, the net reproduction rate of sibling species T1 was higher than that of sibling T2, but the reverse was also true for the proportion of sexual offspring. In the third collection, the proportion of sexual offspring of sibling species T1 was significantly lower than that of sibling species T2. The low density (< 20 ind./L) of the species complex could not lead to compete with each other for food and space resources. Meanwhile, the similar intrinsic rate of population increase (P > 0.05) might contribute to the coexistence of the two sibling species. The disappearance of sibling species T1 on 29 July and sibling species T2 on 5 August from the water body might be attributed to their decreasing net reproduction rate and intrinsic rate of population increase on 22 July and 29 July, respectively. The main reason for the difference in the time of disappearance between the two sibling species might be that all the life table demographic parameters of sibling species T1 were not significantly affected by temperature (P > 0.05), but those of sibling species T2 increased with increasing temperature (P < 0.05).