Feeding selectivities and relative ingestion rates of <i>Daphnia</i> and <i>Bosmina</i>1

TLDR

Differences in feeding behavior are attributed to interspecific differences in morphology and feeding mode. The feeding selectivities and rates of Daphnia rosea and Bosmina longirostris were measured in mixtures of C‑labeled algae and H‑labeled bacteria. Daphnia rosea showed no food preference, whereas Bosmina longirostris displayed variable selectivity (coefficients 2.8–13.7) and, at low food concentrations, ingested 1.6–4.8 times more than Daphnia, suggesting its efficient low‑food feeding and selectivity could challenge competition models based solely on body size.

Abstract

The feeding selectivities and feeding rates of Daphnia rosea and Bosmina longirostris were measured in mixtures of 4 C‐labeled algae ( Chlamydomonas reinhardi ) and 3 H‐labeled bacteria ( Aerobacter aerogenes ) . Daphnia showed no preference for one over the other. Selectivity coefficients (algal clearance : bacterial clearance rate) for Bosmina ranged from 2.8 to 13.7 depending on both previous feeding history and the relative abundance of the two foods. At high concentrations of Chlamydomonas alone the ingestion rates of the two cladocerans per unit body weight were not significantly different, while at low food concentrations (500–10,000 cells ml −1 ) the relative ingestion rate of Bosmina was 4.8 to 1.6× higher than that of Daphnia. Differences in feeding behavior are attributed to interspecific differences in morphology and feeding mode. The ability of Bosmina to feed efficiently at low food concentrations and to feed selectively may invalidate inferences about zooplankton competition from theoretical models of optimal body size alone.