We measured the effects of conspecifics and phytoplankton on the rate at which Epischura lacustris and Epischura nordenskioldi prey upon calanoid nauplii. Per capita predation rates of Epischura in the presence of conspecifics and phytoplankton were 73% lower than those of lone individuals in the absence of phytoplankton. Because these effects occurred at common field densities of Epischura, animal prey, and phytoplankton, it is likely that they occur in situ. Therefore, estimates of the effect of spatial and temporal patchiness on predation rates of omnivorous copepods should consider phytoplankton and conspecifics, not simply the abundance and composition of the animal prey assemblage.

Schulze PC and Folt CL. Limnol. Oceanogr. 34(2):444-450, 1989