Towards a Simple Index Based on Live-Weight and Biomass to Predict Assimilation in Animal Populations

(1) Using published data on energy budgets a simple index is used to derive equations predicting assimilation or production in animal populations. (2) The index is based on the commonly measured parameters of mean annual biomass (cal m-2) and maximum live-weight (mg). The index (Im) is: mean annual biomass (cal m-2)/maximum live-weight (mg)075. (3) The available data relating Im to assimilation can be grouped into five taxonomic categories; homoiotherms (excluding mice and voles), mice and voles, fish, invertebrates (excluding ants), and ants. (4) The invertebrates can be separated by both life-cycle duration ( 2 years) and habitat (aquatic and terrestrial) but too few data are available to analyse separately the combined effects of habitat and life cycle duration. (5) Seven parallel regression lines are derived relating the index (log Im) to assimilation (log A cal m-2 year-1). These lines account for 93% of the variance in the data. (6) The relationship between the index (log Im) and production (log P cal m-2 year-1) is used, with previously derived equations relating production and respiration, to predict assimilation. It accounts for 91% of the variation in the data.