GENERAL-MODELS FOR TROPHIC FLUXES IN ANIMALS BASED ON THEIR BODY-SIZE

Although powerful allometric analyses exist to describe ingestion and respiration for terrestrial vertebrates, a surprising range of organis ms and phenomena have not yet been so analyzed. ANCOVA allows one to f it the heterogeneous literature data for rates of ingestion, growth, d efecation and excretion as functions of body size. In this way, genera l allometric relations with common slopes but different intercepts can be generated for previously unstudied taxa, thereby providing interna lly consistent relations to calculate all components of the balanced g rowth equation. Where comparisons are possible, these relations are si milar to existing relations. Qualitatively, insects are more active th an other ectotherms and birds are more active than other endotherms; e ndotherms perform at higher rates than ectotherms. For all rates, body sizes and taxonomic groupings, the uncertainty of individual predicti on is large, because the rates at any particular size vary. Among diff erent fluxes, median growth rates differ less among gross taxonomic ca tegories than do rates of ingestion, defecation or excretion. Quantita tively, the exponents of size are close to 3/4, but as in previous com parisons, values can be significantly greater or smaller: The 3/4 rule is a statistical rule, not a deterministic one. Nevertheless, despite variations in parameter estimates, most allometric regressions make s imilar estimates of comparable fluxes. For example, these equations al low credible estimates of field metabolic rates that are independent o f the relatively few, measured values available for higher vertebrates , and make promising predictions of field metabolism for other, unstud ied taxa.