Spatial competition in Devonian bioherms of Michigan

F.O. Meyer

University of Michigan, Ann Arbor, Michigan, 48109

Ancient bioherms constitute taxonomically variable paleontologic communities in which biotic components were crowded together in small areas. Under these conditions, competition for living space such as occurs on modern reefs is expected. In Middle Devonian bioherms of Michigan, interspecific spatial competition occurred between blue-green algae, stromatoporoids, and coelenterates. A high growth rate was the major competitive strategy. Very rapid growth permitted blue-green algae to mantle both stromatoporoids and coelenterates and inhibited these organisms from successfully colonizing living algal mats. Similarly, a relative high rate of calcification in stromatoporoids permitted these organisms to overgrow and subsequently exclude coelenterates from becoming permanently established on healthy stromatoporoid colonies. The competitive exclusion of coelenterates by stromatoporoids and both of these organisms by blue-green algae is significant in several respects: 1) Such biologic interactions were capable of controlling the nature of biohermal or reef development, 2) in the absence of severe physical and biologic perturbations to the environment, competitively dominant organisms could monopolize living space and thus produce monospecific biotic zones comparable to those reported within some Paleozoic reefs and bioherms.

Meyer, F. O., 1978, Spatial competition in Devonian bioherms of Michigan: Geological Society of America, v. 10, p. 278.