Ciliate prey and predators.
The rapid 1,400-fold increase in bacterial abundance from day 0 to day 2 was followed by a decline until day 10. We attribute this decline to the grazing by increasing populations of heterotrophic flagellates, naked amoebae, and ciliates (Fig. (Fig.1).1). The numbers of flagellates and amoebae peaked between days 6 and 8, and the number of active ciliates declined after day 10. Hence, the increase in bacterial number after day 10 is probably due to the lower grazing rate. Still, the bacterial population remained high, and depletion of prey is not the reason for the decline of the protozoa. The number of bacteria in the microcosms should be sufficient to ensure maximal protozoan growth. Thus, we hypothesize that internal feedback regulation is a key to understanding protozoan dynamics in soil.