Summer dynamics of egg-ratio of the rotifer Keratella cochlearis (Gosse, 1851) in a eutrophic reservoir: a field study on affecting factors

摘要

The relative strength of factors affecting the egg-ratio (ER) of field rotifer populations and the interactions among them remain poorly studied, nevertheless such knowledge is essential to understand rotifer population dynamics, and production. We present the results of a field study of the summer ER dynamics of the cosmopolitan rotifer Keratella cochlearis (Gosse, 1851), in a eutrophic central Texas reservoir, USA. Relationships between ER and water temperature, Secchi depth, population density, food resources, and potential competitors and predators were studied by single correlation and multiple regression analyses. Low values of ER were concurrent with low and decreasing numbers of the edible phytoplankton fraction and with the increasing number of the inedible fraction suggesting food limitation. ER was significantly correlated inversely with population density and positively with free bacteria and heterotrophic nanoflagellates. No significant correlations were found with abiotic factors and competitors and predators. Significant multiple regression models with the best predictive variables highlighted the importance of intraspecific interactions on ER. Thus, intraspecific interactions and food resources emerged as the main controls acting on the summer ER dynamics of K. cochlearis in this reservoir.