Differences in particle size-dependent feeding efficiencies of closely related rotifer species

Abstract

Size-selective feeding of four Brachionus strains was studied with three experimental setups: selection between polystyrene spheres of different sizes in short-term ( 10 min) fee’ding experiments, selection between pairs of dual-labeled algal taxa in short-term feeding experiments, and selection among three algal taxa in long-term (24 h) feeding experiments. Food size preferences were related to body sizes between strains but not within one strain (Brachionus calyciflorus). Brachionus angularis preferred food items <5-~m equivalent spherical diameter (ESD), Brachionus rubens strain F fed most efficiently on particles -5km ESD, and B. caZycijlorus on particles of lo-pm ESD. Brachionus rubens strain B ingested particles from 3.5 to 12-pm ESD equally well. Apart from particle size effects, feeding was unselective. Polystyrene spheres of the appropriate sizes were ingested readily. Exploitative competition for food is believed to be a major structuring element of zooplankton communities. Consequently, there has been much recent interest in the interspecific role of food Limitation (e.g. Lampert 1985). Herbivorous zooplankton differ in their feeding strategies and modes of food selection (e.g. DeMott 1986; Bogdan and Gilbert 1987), raising the possibility of differential resource use. Within genera, food-size preferences are often related to body sizes. Gilbert and Bogdan (1984) gave evidence for such a pattern from in situ studies with the rotifers Polyarthra and Keratella. Food-size partitioning by differently sized congeners is believed to be an important phenomenon among herbivorous zooplankton (e.g. Hutchinson 1965; Gilbert and Bogdan 1984), and its potential for allowing steady state coexistence was shown in laboratory experiments with the rotifers Brachionus rubens and Brachionus calyciJlorus (Rothhaupt 1988). Rotifers of the genus Brachionus have a cosmo:politan distribution, short generation times, and are easy to culture. They are thus