On weight dependence of net growth efficiency and specific respiration rates among field populations of invertebrates

Annual net growth efficiency (NGE) is approximated here by 100 P _a/(P _a+R _a), P _a and R _a being the annual production and respiration rates of populations per unit area. Published NGE values for 15 temperate invertebrate populations range from 13 to 55%. Contrary to the literature on NGE among speices, the dependence of NGE on species size (as body weight at the onset of sexual maturity, W _s) is not yet determined although the ranges of P _a and R _a, divided by the mean biomass \(\left( {\bar B} \right)\) , approach two orders of magnitude. The \(R_{\text{a}} /\bar B\) rates of 13 of these populations decline with a -0.35 power of W _s rather than the -0.25 power of comparative physiology. A possible reason may be a trend towards larger specimens (relative to W _s or full size) in populations of larger species. Among species, a significant dependence of NGE on W _s (or full size) is not demonstrable for laboratory populations of unicellular organisms and field populations of mammals so that the cost per unit of production might generally be independent of the rate of production by the population.