Interactions Between Predator Kairomone and Food Level Complicate the Ecological Interpretation of Daphnia Laboratory Results

Abstract

The effect of food concentration on the phenotypic response of life history traits to two predator kairomones was investigated in Daphnia. For the experiment, one clone of Daphnia galeata was used as the prey organism and solutions containing infochemicals (kairomones) of Chaoborus (phantommidge) and Perca (perch) simulated the presence of potential predators. The combined effect of food level and predator kairomone on phenotypic plasticity of Daphnia life history is complex. At low food levels, the responses in life history traits to kairomones are enhanced. For example, in the Perca treatment, this leads to a younger age at first reproduction. The presence of Chaoborus kairomone decreases survival so that death often occurs before reproduction is reached. This results in a strong decrease in the intrinsic rate of population increase and might contribut to the pronounced summer decline of some Daphnia populations during periods of food shortage.