LABORATORY STUDIES ON THE POPULATION-DYNAMICS OF ANURAEOPSIS-FISSA (ROTIFERA) IN RELATION TO FOOD DENSITY

1. We offered Scenedesmus obliquus in five densities, from 0.5 to 8 x 10(6) cells ml(-1), to the rotifer Anuraeopsis fissa. Growth rates (r) during the exponential phase (first 7 days) were significantly and positively related to food density. The r values (mean +/- SD) varied between 0.454 +/- 0.067 and 0.856 +/- 0.090, from the lowest to the highest food concentration, respectively. Population growth went through a phase of exponential increase which lasted from 7 to 10 days before a plateau and, in some cases, a decrease occurred. 2. There was a linear relation between food density and rotifer plateau density. At the highest food density, a peak abundance (mean +/- SD) of 2312 +/- 226 individuals ml(-1) was reached, while at the lowest food density there was no identifiable single peak but a plateau, at a density of 361 +/- 62 ind. ml(-1). 3. The egg ratio decreased with increasing population density. The ratio of loose eggs to eggs attached to females indicated that more eggs became detached at higher food densities. 4. As in many other rotifer species studied so far, population density of A. fissa was less stable at higher algal food concentrations. Numerically, A. fissa could be grown at twice the density achieved in Brachionus.