Population Growth of Asplanchna brightwellii (Rotifera) Fed Prey Species Having Different Morphological Defenses

ABSTRACT

We evaluated the population growth of the predator Asplanchna brightwellii fed five different prey (Brachionus angularis, B. rubens, B. patulus, B. havanaensis, and B. macracanthus), singly or in paired combinations. Whereas the first three species of the prey do not possess posterior spines for defense, the last two species have long posterior and/or postero-lateral spines. The growth of A. brightwellii in response to the brachionids differed depending on the morphological characteristics of the prey. A. brightwellii started to reproduce immediately after initiation of the experiments in many treatments. For all prey species except B. macracanthus, increase in food availability resulted in increased peak density and rate of population increase for the predator. Lowest population growth of A. brightwellii was observed when raised on a mixture of B. macracanthus and B. havanaensis. However, A. brightwellii grew well on B. havanaensis alone. Thus, in mixed prey treatments, B. macracanthus may have interfered with predator feeding activity, which led to a lower consumption of the other prey. Regardless of prey type, density, or combination, the peak population densities of A. brightwellii varied from 0.2 to 1.7 ind. mL⁻¹. The rate of population increase (r) varied from 0.025 up to 0.25 per day, depending on the treatment.