Effects of protozoan herbivory and carnivory in a microplankton food web

Abstract

The estuarine ciliates Favella sp. and Balanion sp. both feed on the dinoflagellate Heterocapsa triquetra, and Favella also feeds on Balanion. In laboratory experiments, transient dinoflagellate populations were higher than would be expected if the effects of the 2 grazers were additive; in some experiments the presence of Favella was associated with higher H. triquetra populations. In a theoretical model, increasing the rate of predation on a species could increase that species' steady-state concentration. The relative gross growth efficiencies In this model have an important influence on ecosystem structure. These effects may be important in regulating population densities in microplankton communit~es in which omnivory is common.