Interspecific Competition and Determinants of Extinction in Experimental Populations of Three Rockpool Daphnia Species

The potential importance of interspecific competition for the distribution of three rockpool Daphnia species was examined in a four-year field experiment in artificial rockpools of four different volumes, viz. 4, 12, 50 and 300 l. The three-species, the three two-species combinations, and one-species controls were used. The predictions from island biogeography and metapopulation theory that extinctions rates increase with decreasing patch size and increasing number of species present were also examined. Analyses of reproductive indices and population dynamics indicated that the species used similar resources and that interspecific competition operated during substantial parts of each year