The ecological role of chemical stimuli for the zooplankton: Predator-avoidance behavior in Daphnia

Eight different clones (seven species) of Daphnia had behavioral responses to fish and invertebrate predators. The behavioral response was measured in the laboratory as a change in the average population depth, relative to controls, when exposed to a predator. Behavior for each clone was tested with three common predators: Chaoborus, Lepomis, and Notonecta. Each Daphnia clone responded to at least one predator. Some clones responded to all three predators. The responses are both predator and. prey‐specific. The stimulus produced by the predator is a water‐soluble chemical that persists for up to 7 h in the laboratory. The number of predator species to which a clone responds shows a positive correlation with average body size of the Daphnia. Number of responses per clone is independent of lake size, although there was a tendency (not statistically significant) for the number of responses to decrease with lake size. Behavioral responses may be components of diel vertical migration and horizontal distribution patterns seen in nature.