Population Growth and Body Size in Five Rotifer Species in Response to Variable Food Concentration

ABSTRACT

We cultured five species of rotifers (Brachionus angularis, B. calyciflorus, B. patulus, Euchlanis dilatata, and Lepadella patella) under different algal concentrations (Chlorella vulgaris) for a period of 10 to 15 days, and we derived the rate of population growth per day (r) for each rotifer species. Using a regression between food concentration and the r for each rotifer species, we calculated the minimal food level required to maintain a zero growth rate (threshold food concentration). For all the tested species, there was a direct and positive relationship between food concentration and peak population density. The highest peak density (738 ind. mL^−l) was achieved by L. patella at 0.4X10⁶ cells mL⁻¹. At this food density, B. calyciflorus was only able to reach about 10 ind. mL⁻¹. The highest r value (0.46 d⁻¹) was observed for L. patella at 0.4X10⁶ cells mL⁻¹; at this food concentration, B. calyciflorus and E. dilatata had much lower r values (0.21 and 0.23 d⁻¹, respectively). On a dry weight basis, L. patella had the lowest threshold food concentration (0.0023 mg C t⁻¹ d⁻¹), while B. calyciflorus needed much higher levels (2.04 mg C L⁻¹ d⁻¹). Larger-bodied taxa had higher threshold food concentrations than the smaller-bodied rotifers.