Body Size, Food Concentration, and Population Growth in Planktonic Rotifers

Abstract

Population growth rates of eight species of planktonic rotifers were assessed for five to seven food concentrations using daily renewed batch cultures. The food concentration for which population growth rate was zero (the threshold food level) varied by a factor of 17 among species. The log of threshold food concentration was positively and significantly related to the log of body mass. Similarly, a strong positive log—log relationship was found between rotifer body mass and the food concentration supporting one—half the maximum population growth rate (°max/2); this food concentration varied by a factor of 35 among species. There was a positive relationship between rotifer body mass and maximum population growth rate. Because the smallest species have the lowest threshold food levels and the food levels necessary for them to attain °max/2 are lowest, they appear well adapted to living in food—poor environments. Large species appear to be restricted to food—rich environments but may thrive there because of their high reproductive potential. These conclusions are consistent with observations on species distribution and community structure of rotifers in nature.