Morphological variation and life history changes of a Daphnia hyalina population exposed to Chaoborus flavicans predation (L. Candia, Northern Italy).

The response of Daphnia populations to invertebrate predators involves morphological changes and can lead to a trade-off between growth- and reproduction-related traits. The effects of Chaoborus flavicans larvae on the Daphnia hyalina population in Lake Candia were investigated by comparing the morphometric characteristics and life history traits of the preys during one year with low predator density and one year with a ten fold higher predator density. The increase in Chaoborus density seems to have induced morphological changes in Daphnia hyalina which enabled the modified morph to coexist with the predator. The predator impact did not result in any apparent shift in body size pattern of the prey population, while an increase in average clutch size and a tendency towards a decrease in size at first reproduction suggests the possibility of a predator-mediated shift in life history traits.