Abstract

Size selectivity spectra of 28 planktonic predators from 18 studies in the literature are compared. The linear size ratio between predators and their optimal prey is 1 : 1 for a dinoflagellate, 3 : 1 for other flagellates, 8 : 1 for ciliates, 18 : 1 for rotifers and copepods, and ∼50: 1 for cladocerans and meroplankton larvae. These size ratios seem consistent within groups, and their validity is supported by quantitative information from the literature. However, a difference between filter feeders and raptorial‐interception feeders, preferring relatively smaller and larger prey respectively, is evident across the taxonomic groups. A classification of planktonic predators into functional groups is therefore crucial for the construction of models of pelagic food webs.