Effect of the cyclopoid copepod Mesocyclops thermocyclopoides on the interactions between the predatory rotifer Asplanchna intermedia and its prey Brachionus calyciflorus and B. angularis

Abstract

In many shallow, eutrophic subtropical ponds, brachionid rotifers are common prey of the predatory copepod Mesocyclops thermocyclopoides. The predatory rotifer Asplanchna intermedia, which is itself a potential prey of the copepod, also feeds preferentially on brachionids. We studied in the laboratory the population dynamics of two mutually competing prey species, Brachionus angularis and B. calyciflorus, in the presence of the two predators A. intermedia and M. thermocyclopoides. The experimental design included separate population dynamics studies with one prey-one predator, two prey-one predator, one prey-two predator, and two prey-two predator systems. These combinations were compared with controls, in which both the prey species (B. angularis and B. calyciflorus) were grown separately and in combination with each other. In the absence of any predator, B. angularis generally eliminated the larger B. calyciflorus. Selective predation by the copepod allowed B. calyciflorus to persist longer in competition with B. angularis. Feeding by M. thermocyclopoides on A. intermedia reduced the predation pressure on B. calyciflorus. However, given enough time, the cyclopoid copepod was able to eliminate both the brachionids as well as the predatory Asplanchna.