The effect of food concentration on swimming patterns, feeding behavior, ingestion, assimilation, and respiration by Daphnia1

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Abstract
Swimming patterns, feeding behaviors, and ingestion, filtering, assimilation, and respiration rates were measured for Daphnia magna in food concentrations from 0 to 106 Chlamydomonas reinhardi cells·cm−3, equivalent to 0–20 mg C·liter −1. A Holling type 2 functional response curve or an Ivlev model without a threshold appear to be biologically meaningful descriptions of Daphnia feeding response to different food concentrations. Daphnia has no feeding threshold or reduced filtering activity at low concentrations such as are predicted by optimal foraging models. Above the incipient limiting concentration, constant ingestion rates and an over‐collection of food result in increased rejection rates. These behaviors may cause high respiratory rates and reduced net assimilation rates at the highest food concentration. Daphnia does not orient to or alter swimming patterns in response to algal patches.