The effect of food quality on feeding and respiration by Daphnia and Diaptomus1

Abstract

Filtering, ingestion, and respiration rates for Daphnia pulex and Diaptomus siciloides were measured in southern Green Bay water mixed with algal cultures to produce varying proportions of blue‐green algae. These measurements along with observations of Daphnia mouthpart responses to these foods were used to assess the relative competitive potential of Daphnia and calanoid copepods in lakes of varying trophy. Ratios of filtering and ingestion rate to respiration rate were used as a measure of energy input per unit of energy expended. Passive filtering and subsequent rejection of inedible algae by Daphnia result in higher ratios than those shown by Diaptomus in high quality foods, suggesting a competitive advantage in oligotrophic or mesotrophic lakes. Diaptomus selective feeding, on the other hand, results in higher ratios in the low quality food characteristic of eutrophic conditions. These results and data from the literature are used to propose a two‐dimensional niche model to demonstrate the interaction between food quality and abundance on the competitive interaction between calanoid copepods and Daphnia ‐like cladocerans.