Journal of Plankton Research Vol.22 no.10 pp.1925-1944, 2000
© Oxford University Press 2000
The influence of autotrophic and heterotrophic foods on the demography of Daphnia longispina under starved, semi-natural and enriched conditions
Maison de la Recherche, Université Blaise Pascal, UPRES A 6042 CNRS, 4 rue Ledru, 63057 Clermont-Ferrand, Cedex, France
We tested the influence of different types of food on the fitness of Daphnia longispina during a period of poor resources by comparing the growth and reproduction of individuals fed on different diets. When Daphnia were under starvation conditions, both dissolved organic carbon and metabolic products enhanced bacterial growth, and the cladoceran produced 15 neonates and survived for the 55 days of experiment. In the natural water, the edible food consisted essentially of bacteria and heterotrophic flagellates, which enabled the cladoceran to grow and reproduce. In water enriched with Cryptomonas (an alga) or Chilomonas (a heterotrophic flagellate), the daphnid growth rates increased considerably from generation to generation, but later in the time course of the experiment with Chilomonas than with Cryptomonas. This alga enhanced the phosphorus:carbon ratio. The primiparous daphnids fed with Cryptomonas were smaller than those fed with the heterotrophic flagellate and enrichment with the heterotrophic flagellate also enhanced reproduction. In Lake Tazenat, when the algal biomass was insufficient to support the Daphnia life cycle, the heterotrophic organisms were an essential food source. When feeding essentially on bacteria, Daphnia has the capacity to grow and reproduce at very low food concentrations, and this is important in determining its fitness under competitive conditions.