Adult Body Mass and Annual Production/Biomass Relationships of Field Populations

We investigate specific production rates (per unit biomass) of populations using published data on the relation of annual production/mean biomass (P/B). Aquatic and terrestrial invertebrates between the sizes of copepods and clams are emphasized, ranging about 10 5 —fold in body mass upon reaching maturity (M s , in kcal to compare with respiratory energy expense) and about 10 2 —fold in P/B. Fishes and mammals are briefly treated; phytoplankton is mentioned. For 33 invertebrates living at annual mean temperatures between about 5° and 20°C, M s is shown to be an efficient and precise estimator, or scaling factor, of the annual P/B. The rate declines markedly with M s according to P/B = 0.65M s — 0 . 3 7 . The exponent differs significantly from the —0.25 power of comparative physiology. Most of the measured values of P/B fall within 50 to 200% of predicted values. Much of this variability is associated with the ratio of annual production/annual respiration (P/R): for a given M s , species achieving about half the predicted P/B have P/R ratios of about 0.1; those achieving twice the predicted P/B have P/R ratios of about 1.0. Age upon reaching maturity contributes some variability, with late—maturing (>1 yr) species tending towards a higher P/B. The variability is not significantly correlated with phylogenetic relationships (excepting insects for which P/B might not be mass—dependent), trophic type, major habitat, production rate, or biomass of the populations. The values of P/B of invertebrates living at annual mean temperatures >25° may be elevated over those of temperate species of the same M s , while those of polar forms are depressed. The reasons for a single power function governing the mass dependence of P/B of temperate invertebrates, and for the particular exponent, are unclear; an ecological cause, i.e., mortality, combining with the general size dependence of life processes, is implicated. On the average, the annual specific mortality rate equals P/B and hence also declines by 0.65M s — 0 . 3 7 . Very small metazoans (pelagic rotifers, benthic meiofauna) tend to have an appreciably lower P/B than indicated by the relationship for larger invertebrates. A refuge from predation by being small is postulated which may also apply for phytoplankton. For meiofauna, a power function of mass dependence of P/B with average rates 3—5 times below those of the larger invertebrates is suggested. Annual P/B values of fishes and mammals likewise decline by a power function of M s ; the few available data yield exponents of —0.26 and —0.33, respectively. Ecological reasons are again invoked. Values of P/B and the specific mortality rates of temperate fishes seem to be 4—5 times, and those of mammals 20—25 times, higher than those of temperate invertebrates of the same mass.