Combined effects of temperature, food availability and predator's (Asplanchna girodi) allelochemicals on the demography and population growth of Brachionus havanaensis (Rotifera)

We studied the influence of asplanchnin (a non-toxic kairomone from the predator Asplanchna girodi) on the selected populations of prey Brachionus havanaensis cultured at two algal densities (0.5x10⁶ cells mL⁻¹ and 2x10⁶ cells mL⁻¹ of Chlorella vulgaris) and at two temperatures (15° and 25°C). At 15°C, the allelochemicals decreased the survival and offspring production of B. havanaensis at same food levels. Both gross and net reproductive rates were about 50% lower at 15°C than at 25°C. In the absence of asplanchnin, the rate of population increase (r) was highest (0.52 per day) at 25°C under 2 x 10⁶ cells mL⁻¹ of Chlorella. While in the presence of asplanchnin, the r was negative (−0.09 per day) at 15°C, at 0.5 x 10⁶ cells ⁻¹. At higher temperature and higher food density, life history variables of B. havanaensis did not show adverse impact of asplanchnin. At 15°C under two food levels, B. havanaensis populations decreased in the presence of asplanchnin. However, at 25°C, B. havanaensis grown at low food level showed similar population densities (ca. 100 ind. mL⁻¹) regardless of the presence of asplanchnin. At 25°C and high food level, B. havanaensis had very low densities in the presence of Asplanchna than in controls. Thus, we showed the importance of food density and temperature as variables to evaluate the impact of predators’ allelochemicals on the prey demographic characteristics.