Combined effects of temperature and lead concentration on the competition between the rotifers Brachionus havanaensis and Brachionus rubens (Rotifera: Brachionidae).

The combined effects of temperature (22 and 32 degrees C) and the concentration of Pb (0, 0.05, 0.1 and 0.2 mg L- 1) on the competition between B. havanaensis and B. rubens using population growth was evaluated. At 22 degrees C, increase in Pb concentration had little effect on the population growth of B. havanaensis, while it had adverse effect on B. rubens. At this temperature, the presence of B. rubens had adversely affected the growth of B. havananensis. However, under similar conditions, B. rubens was not influenced by B. havanaensis. Increase in Pb concentration decreased the population growth of B. havanaensis at 32 degrees C regardless whether the population was alone or together with B. rubens. When grown alone, B. havanaensis was numerically more abundant than B. rubens. B. havanaensis grown at 32 degrees C had population growth rates of 0.32 to 0.56 day- 1, depending on Pb level and the presence of competitor. At this temperature, B. rubens had mostly negative growth rates. Further, our study showed that Pb at a concentration as low as 0.05 mg L- 1 had adverse effect on B. rubens at both the temperatures. Though B. rubens is known to occur naturally at wide temperature range, in our study this species appeared to have adapted to low temperature.