Predator-induced life history shifts in Daphnia:: a synthesis of studies using meta-analysis

Daphnia respond to kairomones from a variety of predators by altering their morphology, behavior, and life history. I use the statistical technique of meta-analysis to quantitatively evaluate the results of 27 independent studies that examine various life history responses of Daphnia to kairomones released from three common predators: Chaoborus, Notonecta, and planktivorous fish. Daphnia exhibit a fundamentally different set of life history responses to Chaoborus (delayed reproduction, decreased size of first clutch, slight tendency toward increased size at maturity) than they do to Notonecta and fish (earlier reproduction, increased clutch size, smaller size at maturity). These opposite responses appear to be related to different patterns of prey selection exhibited by the predators. Food level does not affect the life history responses of Daphnia to Chaoborus kairomones; however, the length of exposure to these kairomones does influence the degree of delay in reproduction. In addition, changes in size at maturity in response to predator kairomones are positively correlated with changes in both age at maturity and size of the first clutch. While the life history shifts exhibited by Daphnia in the presence of Notonecta and fish appear to be clearly adaptive, the fitness consequences of Chaoborus-induced responses are unclear.