Ecological Energetics of a Natural Population of the Predaceous Zooplankter Leptodora kindtii Focke (Cladocera)

Abstract

Parameters for natural populations of the fluidfeeding predaceous zooplankter Leptodora kindtii and probable prey species were followed for three years against a background of limnological monitoring of a shallow lake ecosystem, Sanctuary Lake, Crawford County, Pennsylvania. Due to the shallow, uniform nature of the Fish Hatchery Bay portion of Sanctuary Lake, physical-chemical conditions are quite homogeneous during the Leptodora growing season (May through November). Oxygen is normally near saturation, water temperatures follow air temperatures closely and the system is highly productive. Bluegreen algae dominate the phytoplankton during the summer and fall. The population parameters finite birth, instantaneous birth, instantaneous population change, and instantaneous death rates were estimated from field data for six possible prey species (four cladocerans and two copepods). Also, turnover and production rates were calculated for the prey. The same population data were gathered for Leptodora, and predator - prey inferences were drawn by comparing Leptodora birth rates with prey death rates. The results indicate that the predator - prey relationships are quite complex, with the Leptodora population usually depending on at least two prey species at any given time. Annual production for the Leptodora population was 0.362 g/m3 (1876.1 cal/M3) in 1966 and 1.427 g/m3 (7395.4 cal/M3) in 1967. Assuming assimilation and production (i.e. growth plus reproduction) efficiencies to be 40 % and 30 % respectively and calculating yield from estimates of death rate (d), annual energy budgets for