Population dynamics of food‐limited rotifers in two‐stage chemostat culture1,2

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Abstract
The population dynamics of Brachionus calyciflorus were studied in two‐stage chemostat cultures. Chlorella pyrenoidosa was supplied continuously from a steady state culture growing with constantillumination onlimiting nitrate. Rotifer growth in the second stage (in the dark) was limited by the rate of supply of algae. The algal supply rate and rotifer specific growth rate, µ, were determined by the second‐stage dilution rate, D(µ = D in the steady state). Population densities and size‐age structures were determined with an electronic particle counter. Small body size and obligate amictic females apparently were selected in these chemostats. The growth rates observed were the highest yet recorded for any species of Brachionus.The chemostat system facilitated unambiguous determinations of rotifer growth and fecundity, since food was supplied and wastes were removed at continuous, controlled rates. Specific ingestion and loss rates, yield (netrotifers produced/algae ingested), production (rotifers produced·h−1), and rotifer standing crop increased directly with µ. Although most observations are qualitatively similar to data from heterotrophic microbial chemostat studies, a close fit to the rotifer steady state observations was obtained only when K was assumed to be variable (an inverse function of µ) rather than constant. Numerical simulations of the same model only approximately reproduced transient data. Microbial growth models may be useful to represent rotifer growth at or near steady state but are inadequate to explain moderate to large transient fluctuations of populations.