The power of size: A meta-analysis reveals consistency of allometric regressions

The recent revival of body size relationships in ecology has boosted our understanding of ecosystems. Here, a simple model, based on energy equivalency, integrates rate, age, density and area parameters that are important in ecological modelling. Allometric relationships for quantities as diverse as ingestion, mortality; age at maturity, maximum density territory size of different species groups and trophic levels are derived from production and some ecological transfer efficiencies. The theory is supported by a meta-analysis of 230 allometric regressions derived from over 100 publications. The relationships are shown to be mutually consistent and fit into the model. Rate constants generally decrease with organism mass at an exponent of -1/4. Age and density parameters increase in the same direction following a slope of 1/4. Differences between plants, invertebrates, cold-blooded vertebrates and warm-blooded vertebrates are reflected in the intercepts and can be anticipated from temperature, trophic position and evolutionary history. Cold-blooded species have lower rate constants but reach higher ages and densities than equally sized warm-blooded organisms. Intercepts of body size distributions tend to decrease with trophic position, at a level that is predicted by ecological efficiencies. Area parameters, such as the territory size and geographic range, tend to decrease with species size, but slopes and intercepts were often different from the expected value. Occasionally, outliers were also noted for rate, time or density parameters. With the model at hand, such deviations can be easily identified and subjected to more extensive empirical and theoretical research. With these restrictions, specific issues can now be addressed by a framework that complies with extensive information on related parameters. (c) 2007 Elsevier B.V. All rights reserved.