No abstract

Lake Washington received increasing amounts of secondary sewage effluent from 1941 to 1963 and responded by changes in the amount of nutrients in the water and in the kind and quantity of phytoplankton.From 1963 to 1968 the amount of effluent entering the lake was progressively decreased to zero, and the lake promptly responded with decreases in the amount of nutrients, the quantity of phytoplankton, and the proportion of blue-green algae.

In 1976 Daphnia, a genus that had been inconspicuous in the zooplankton of Lake Washington, suddenly became dominant. The mean summer transparency of the lake doubled. The major change affecting the SUCCESS of Duphniu evidently was a decrease in the abundance of the predatory Neomysis mercedis in the mid-1960s. Daphnia probably did not increase at that time because of the continued persistence of significant quantities

1. A graphical model is described with which one can calculate for any reproductive schedule values for population growth rate, birth rate, death rate, egg ratio, and age structure. Variations are discussed to describe different kinds of life history. 2. Examples are described to show how various population parameters are interrelated and how they vary with reproductive schedule. Discrepancies that arise in deriving instantaneous coefficients from counts of a population growing by discrete steps are noted.