Cladoceran body size and vulnerability to copepod predation

We examined species-related and age-related mortality caused by a predaceous copepod (Acanthocyclops robustus) in five closely related cladocerans representing a wide spectrum of body size. Animals of all five species from clonal cultures were exposed for 1, 2, or 4 d in medium from a copepod-infested enclosure that either did or did not contain natural densities of Acanthocyclops adults and copepodites (40-50 copepods liter-1). In each of the five species, the 1-d-old neonates were most, and adults least, vulnerable to the copepods. Small-bodied Daphnia cucullata and Ceriodaphnia reticulata remained vulnerable until maturation, but the susceptibility of large Daphnia magna drastically decreased in 3- and 5-d-old animals, and 7-d-old adults were immune to copepod predation