Food dependence and energetics of freeliving nematodes : II. Life history parameters of Caenorhabditis briggsae (Nematoda) at different levels of food supply.

The food dependence of larval duration, fecundity and the intrinsic rate of natural increase follow a hyperbolic form, which can for the former be described by the Michaelis-Menten function.Maximal larval duration at 20° C is 62 h, maximal fecundity is 153 eggs per female and r max is 1.136 per day. The lower food threshold is 108 E. coli cells·ml-1 (=0.06 mg dry weight·ml-1) for larval growth and 2·108 cells·ml-1 for reproduction and "r". 50% of maximal performances (K s ) are attained at 5·108 and 7.5·108 cells·ml-1 respectively.Reproductive effort at dense food is highest immediately after maturation (e.g. 50% of the total eggs produced by a female are laid within 2 days after onset of egg production). At lower food densities the reproductive effort is delayed.Larval mortality increases strongly below 109 cells·ml-1.The results reported sofar were obtained with E. coli cells which were harvested at the phase of decreasing population growth in batch cultures. With cells from the exponential and the stationary phase, performances are increased and decreased respectively. This is partly due to differences in bacterial biomass per unit cell, partly an expression of the change of nutritive value of bacterial cells with growth phases.