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.