Biotic Interactions and Siliceous Marine Phytoplankton

Unlike most organisms, marine phytoplankton experience nearly deterministic rates of biotic interactions mediated by stochastic rates of turbulence. Yet studies of phytoplankton evolution have largely ignored biotic interactions, whereas studies of phytoplankton ecology have largely ignored evolutionary constraints. This review will attempt to integrate the opposing and complementary selective forces experienced by phytoplankton due to biotic and abiotic parameters over ultimate (evolutionary) and proximate (ecological) time scales. Attention will be focused on biotic interactions experienced by siliceous phytoplankton and the influence of these interactions on coexistence and local extinction (the ecological time framework), and diversification and species selection (the evolutionary time framework). The principal topics of discussion include the significance of biotic interactions among phytoplankton to the mechanisms of species displacement, species coexistence, the maintenance of species diversity, the selection of life history characteristics, and the mode and rate of evolution. A case study developed from a Paleogene phytoplankton assemblage is presented to illustrate that understanding the mechanisms of species interactions is requisite to a comprehensive interpretation of temporal changes in morphology, species dominance, and diversity. [For reviews of the physiology, ultrastructure, and distribution of siliceous marine phytoplankton, the reader is referred to Werner (1977), Bold and Wynne (1978), Morris (1980), Falkowski (1980), and Tappan (1980)].