Allelopathic interactions between the predator (Asplanchna brightwellii) and prey (Brachionus calyciflorus) for coexistence

An allelopathic interaction between the predators and prey is an important mechanism to structure the zooplankton in freshwater ecosystems. Invertebrate predation on planktonic communities depends on several factors (but major ones are defences and reproductive capacity of prey organisms). We evaluated the effects of different densities of herbivorous prey B. calyciflorus on the population growth of its predator A. brightwellii. Prey at four initial densities (1.25, 2.5, 5 and 10.0 ind. mL⁻¹) and predators at one density (0.05 ind. mL⁻¹) were grown together using the singlecelled alga Chlorella vulgaris at two concentrations (0.5X10⁶ and 2.0X10⁶ cells mL⁻¹). In the absence of predators (regardless of initial density), increase in algal food concentration promoted the population abundances of B. calyciflorus. In the presence of allelochemicals from predators, the population of B. calyciflorus was decreased at all initial densities (except at inoculation density of 10 ind. mL⁻¹, and high food level) but its population had positive growth. Predator's peak population density continued to increase with the availability of B. calyciflorus but remained stationary, when prey was cultured at high inoculation density and high algal food level. Thus, under conditions of high food level and high inoculation density of prey, the coexistence of B. calyciflorus with A. brightwellii was possible; however, the field verification is still needed.