Factors influencing Diaptomus distributions: An experimental study in subtropical Florida 1

In central and southern Florida Diaptomus dorsalis is the sole diaptomid in most eutrophic lakes whereas Diaptomus floridanus and Diaptomus mississippiensis co‐occur in oligotrophic and mesotrophic lakes. The importance of food availability and water quality in determining the species distributions of Diaptomus was ascertained by culturing the three species in water from a lake of each type with its natural phytoplankton present and with the natural phytoplankton removed and Chlamydomonas added at a concentration above feeding saturation. The experimental evidence indicated that neither food availability nor water quality is important in excluding D. floridanus and D. mississippiensis from the eutrophic lakes. Additional data suggested that strong predation pressure may prevent these two species from occupying lakes of this type. However, low food availability seemed of major importance in excluding D. dorsalis from the oligotrophic and mesotrophic lakes. Competition is likely because food levels are always limiting and a potential competitor is present in the form of D. floridanus —in the same subgenus and close to the same size. Additional evidence suggests that predation is probably of lesser importance to the zooplankton in lakes of these types.