The most basic, 'type 1' functional response is that assumed by the Lotka-Volterra equations: consumption rate rises linearly with prey density (indicated by the constant, a, in Equation 10.2). An example is illustrated in Figure 10.8. The rate at which Daphnia magna consumed yeast cells rose linearly when the density of cells
varied, because the yeast cells were extracted by the Daphnia from a constant volume of water washed over their filtering apparatus, and the amount extracted therefore rose in line with food concentration. Above 105 cells ml-1, however, the Daphnia could filter more cells but were unable to swallow all the food they filtered. They therefore ingested food at a maximum (plateau) rate irrespective of its concentration.
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