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

Abstract

Saccharomyces cerevisiae labelled with P32 was fed to Daphnia magna and Feeding rate of Daphnia was calculated from uptake of P32. Errors inherent in the method were measured and discussed. An unexpected source of error was due to a rapid uptake of P32 during the first few minutes in high concentrations of yeast. An hypothesis is presented to explain this phenomenon.In concentrations of yeast below 105 cells/ml, feeding rate of Daphnia magna is proportional to concentration of food. As concentration of yeast is increased above 105 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.