The Filter-Feeder as an Optimal Forager, and the Predicted Shapes of Feeding Curves

If a filter-feeder is assumed to maximize the net rate of energy gained from its food, then the theoretically predicted relations between filtering rate, ingestion rate, and the abundance of food agree with empirical models at high concentrations of food cells, but not at low particle densities where experimental results are scarce. A general model is derived for filter-feeding behavior in mixtures of particle types and is used to evaluate selective ingestion of particles based on their comparative abundances, sizes, and digestibilities. Filter-feeders are predicted to harvest optimally in a mixture if their rates of ingestion are maximal for particles slightly larger than those most numerous in the mixture. Conditions which could lead to the passage of viable cells of some species of algae through the gut of a filter-feeder are examined.