THE EFFECT OF FOOD ON PROTEIN-CONTENT IN ROTIFER AND CLADOCERAN SPECIES - A FIELD CORRELATIONAL STUDY

1. The protein content of individuals of four species of cladoceran and two species of rotifer in eight ponds was measured over several time periods. The protein content in coarsely filtered water, which includes particulate (less than 31-mu-m for cladoceran and less than 10-mu-m for rotifers) and dissolved proteins, was also analysed to estimate the amount of food available to the animals. 2. A positive relationship between protein content of individuals and protein in the food was found for all the species. The increase in protein content of the animals was less pronounced when food was more abundant. 3. When food concentration was lower, a greater reduction in protein content was observed in two species of rotifers than in four cladoceran species. Moreover, when comparing among species of Cladocera, the reduction in protein content at low food concentrations was more marked in the small-bodied than in the large-bodied species. These results are consistent with the size-efficiency hypothesis.