FACTORS AFFECTING THE PRODUCTION OF ZOOPLANKTON IN LAKES

Multiple regression analysis and analysis of covariance were used to a ssess the degree to which observed variation in rates of production am ong 108 lake zooplankton populations could be accounted for by variati on in physical and biological factors. Seventy-six percent of the obse rved variation in growing season weight-specific production rates coul d be accounted for by differences in temperature, length of growing se ason, and taxonomic group (Rotifera, Chydoroidea, Cyclopoida, Calanoid a, ordered from highest rate to lowest). Within taxonomic groups, effe cts of population biomass density, individual body size, and food avai lability were not detected. Fifty-eight percent of the observed variat ion in growing season population biomass density could be accounted fo r by differences in individual body size, mean chlorophyll concentrati on, and lake mean depth. Twenty-four percent of the observed variation in growing season length could be accounted for by differences in mea n chlorophyll concentration and taxonomic group. Our findings suggest a simple model of the seasonal production cycle for limnetic zooplankt on in which weight-specific rates of biomass production are largely se t by temperature, and levels of biomass accumulation are largely set b y food resource availability and individual body size. We briefly disc uss the implications of this model for predicting the effects of clima te change on lake productivity.