THE RELATION BETWEEN CONCENTRATION OF FOOD AND FEEDING RATE OF DAPHNIA MAGNA STRAUS

Abstract

Saccharomyces cerevisiae labelled with P 32 was fed to Daphnia magna and Feeding rate of Daphnia was calculated from uptake of P 32 . Errors inherent in the method were measured and discussed. An unexpected source of error was due to a rapid uptake of P 32 during the first few minutes in high concentrations of yeast. An hypothesis is presented to explain this phenomenon.In concentrations of yeast below 10 5 cells/ml, feeding rate of Daphnia magna is proportional to concentration of food. As concentration of yeast is increased above 10 5 cells/ml the feeding rate increases very slightly or not at all. These results are discussed in relation to the supposed inhibition of feeding by high concentrations of log-phase Chlorella suggested by Ryther, and Cushing's 'encounter theory' of grazing.