Zoological Studies

Impacts of Predation by the Copepod, Mesocyclops pehpeiensis, on Life Table Demographics and Population Dynamics of Four Cladoceran Species: a Comparative Laboratory Study

Jiang-Shiou Hwang, Ram Kumar, and Chung-Su Ku (2009) Predation is a major source of prey mortality in which the goal of the predator is to maximize the efficiency with which it can ingest its prey while that of the prey is to develop strategies to minimize mortality due to predation.  Copepods are dominant invertebrate predators in tropical freshwater ecosystems.  The evolutionary responses to copepod predation pressures are not known in tropical systems.  The predatory copepod, Mesocyclops pehpeiensis, is numerically abundant and exerts major predation pressures on different cladoceran species in tropical and subtropical freshwater systems.  We investigated in the laboratory the responses of 4 cladoceran species: Scapholeberis kingii, Ceriodaphnia cornuta, Moina macrocopa, and Daphnia similoides to the copepod Mes. pehpeiensis.  Two experiments were conducted: (a) life table demographics in a control and in water preconditioned by the copepod, and (b) population dynamics in a control, in the presence of the copepod, and in water preconditioned by the copepod.  With the exception of S. kingii, average reproductive rates in the other 3 cladocerans were significantly higher in copepod-conditioned water than in the control.  Furthermore, D. similoides showed a higher increase in reproductive rates in copepod-conditioned water than did the other 3 cladoceran species.  The presence of the copepod severely suppressed the population growth trajectories of all 4 cladoceran species tested.  The copepod-imposed reduction in population growth rates was significantly higher for Moi. macrocopa and S. kingii.  With the exception of S. kingii, the other 3 cladocerans reproduced earlier in the copepod treatment.  The neonate size at hatching and maximum body sizes reached by the 3 cladocerans (except S. kingii) in treatments were larger than those in the controls.