Size-Selective Feeding by the Predatory Copepod Epischura lacustris Forbes

Abstract

Size-selective predation by Epischura lacustris on Bosmina longirostris was investigated in the field by comparing the size distributions of Bosmina available in the water column with the carapace sizes of killed Bosmina. While Epischura could consume the entire size range (0.2–0.4 mm) of Bosmina, smalt prey (0.2–0.25 mm) consistently constituted the greatest portion of the diet. For Bosmina, vulnerability depended on the rate of encounter with the predator and on the probability of ingestion by the predator. The frequencies of different-sized prey in the diet were partially predicted on the basis of their relative abundance weighted by their ingestion probabilities. The prediction could be improved if encounter rates were known.