WILLIAM C. WOLFINBARGER, University of Oklahoma, Department of Zoology, 730 Van Vleet Oval, Room 314, Norman, Oklahoma 73019-0235, USA

I took weekly samples of zooplankton, phytoplankton, and primary productivity at four sites in Hugo Reservoir, Oklahoma between March and September 1996. My objectives were to assess the importance of producer abundance on the structure of the cladoceran populations. Limnological parameters (water temperature, phytoplankton abundance, and primary productivity) were used to predict zooplankton population parameters (abundance, egg ratio, and production) using multiple regression models. Preliminary results indicate that early in the year, as water temperature increased, Bosmina longirostris was the dominant cladoceran species. In June, as water temperatures exceeded 25^oC, blue-green algae increased in abundance. Bosmina longirostris abundance declined and Ceriodaphnia lacustris, Diaphanosoma spp., and Moina spp. abundance increased.