THE SIZE RATIO BETWEEN PLANKTONIC PREDATORS AND THEIR PREY

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 approximately 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.