Abstract: By the method of population accumulative culture, this paper studied the effects of different concentration (0.03, 0.3, 3.0, 30 and 300 μg·L^-1) of dicofol and different algal food densities (3.0 and 5.0×10⁶ cells·ml^-1 of Scenedesmus obliquus) on the population growth of rotifer Brachionus calyciflorus. The results showed that dicofol concentration, algal food density, and their interaction had significant effects on the population growth rate of the rotifer (P<0.05). Both algal food density and dicofol concentration affected the maximal population density (P<0.01) significantly, but the reverse was found for their interaction (P>0.05). Compared with the control, when the algal density was 3.0×10⁶ cells·ml^-1, the population growth rate of the rotifer had a significant increase at 0.03-30 μg·L^-1 of dicofol, and its maximal population density was decreased at 3 μg·L^-1 of dicofol but increased at 300 μg·L^-1 of dicofol significantly. However, when the algal density was 5.0×10⁶ cells·ml^-1, dicofol had no significant effects both on the population growth rate and on the maximal population density of the rotifer. The results suggested that higher algal food densities mitigated the stimulating effects of dicofol at 0.03-30 μg·L^-1 and 300 μg·L^-1 on the population growth rate and maximal population density of B. calyciflorus, and the repressing effect of dicofol at 3 μg·L^-1 on the maximal population density of the rotifer.

Key words: Multiple ecological niche of one-species (variety) (MENOS), Niche breadth, Niche overlap, Cotton