Effects of Mesocyclops thermocyclopoides (Copepoda: Cyclopoida) predation on the population growth patterns of different prey species

The omnivorous cyclopoid copepod, Mesocyclops thermocyclopoides, perennially found in many lakes and ponds of Delhi, preys on a variety of zooplankton species ranging from protozoans to crustaceans, but its impact on the population dynamics of the prey is variable. I studied in the laboratory the population growth patterns of selected prey species of different taxa-ciliates (Stylonychia notophora, Paramecium caudatum and Pseudourostyla levis), rotifers (Brachionus angularis, B. rubens and B. calyciflorus), and cladocerans (Ceriodaphnia cornuta, Moina macrocopa, and Daphnia similoides) in the presence and in the absence of M. thermocyclopoides. I used the intrinsic rate of natural increase of the prey and a predator impact index to assess the impact of cyclopoid predation. The predator impact was significantly higher on protozoans and cladocerans than on rotifers. The most adversely affected species were C. cornuta, P. caudatum and B. calyciflorus, and the least affected were D. similoides, B. angularis and P. levis. The mortality imposed by the copepod was significantly less (or no mortality) on the seventh day than on the third day in each case. My laboratory studies suggest that the differential impact of predation by M. thermocyclopoides may be one of the determinants of zooplankton community structure in shallow, eutrophic subtropical and tropical water bodies.