Body Size, Energy Reserves, and Competitive Ability in Three Species of Cladocera

Abstract

The purpose of this study was to identify mechanisms of competitive ability among planktonic Clodocera. We used three species (Daphnia magna, Daphnia galeata, and Bosmina longirostris) in life—table and birth—schudle experiments to analyze the effect of low food levels on each population, and in competition experiments. Demographic traits of all species were affected by low food levels, but the smaller species suffered higher death rates. D. magna matured and reproduced well in the lowest food level studied; growth rate of the population was 0.143 d—1. Survivorship for D. galeata cohorts was poor at the lowest food level but many animals did mature and reproduce; population growth rate was 0.082 d—1. Few Bosmina individuals matured and reproduced and all were dead by the third adult instar; the population growth rate was —0.136 d—1. In the competition experiments, D. magna was the numerical dominant in high—food cultures with D. galeata, and D. galeata was the numerical dominant in cultures with Bosmina. ...