RESOURCE DEPRESSION IN DAPHNIA-GALEATA, DAPHNIA-CUCULLATA AND THEIR INTERSPECIFIC HYBRID - LIFE-HISTORY CONSEQUENCES

In this study, the effect of the food concentration on several life hi story parameters of Daphnia galeata, Daphnia cucullata and the hybrid between these two species was examined. The food concentration had a s ignificant effect on both growth and reproduction of all three taxa. M ortality was highly species specific, and to a lesser extent dependent on the food concentration. Changes in life history parameters resulte d in changes in the intrinsic rate of population increase (r). The foo d dependence of the different species was found to be different. Daphn ia cucullata had a relatively constant and low v. The r values for the hybrid varied most, with low values compared with the parental specie s when grown at low food levels and relatively high values at higher f ood concentrations. Our results suggest that when food concentrations are high the hybrid will have a selective advantage over both parental species, but that at lower food levels D.galeata will have an advanta ge over both D.cucullata and the hybrid.