Allometric scaling at higher levels of biological organisation: Evidence from natural aquatic microcosm ecosystems.
Hayward, April*,1, Kolasa, Jurek1, 1 McMaster University, Hamilton, ON, Canada
ABSTRACT- Allometric relations are pervasive in nature and have been found at a variety of levels of biological organisation. Most allometric patterns found at higher levels of biological organisation – such as populations and communities – are generally reducible to additive functions of organism-level allometric patterns of resource use: most higher-level patterns have been mathematically explained as direct consequences of the well-known relation between metabolic rate and body mass in organisms. As an additional consequence of such organism-level allometric patterns of resource use, total ecosystem energy use per unit ecosystem size is predicted to be invariant (i.e. slope = 0) with ecosystem size. To test this prediction we used the dark bottle method to estimate ecosystem respiration rate in natural, multi-trophic aquatic rock pool microcosms at Discovery Bay, Jamaica in January 2005. Ecosystem respiration rate was not invariant with ecosystem size but, rather, was slower in larger pools. Specifically, ecosystem respiration rate was found to scale as a function of ecosystem size (rock pool volume) to the power of -0.28 (n=30, r2 = 0.40, p<0.0001, CL± 0.10). Curiously, the slope of the relation found here is statistically indistinguishable from -0.25 (the analogous slope found for organisms). A slope of approximately -0.25 for the relation between ecosystem metabolism and ecosystem size is expected only if organism density does not scale with organism size in every individual microcosm ecosystem in the study. Evidence from a number of other studies suggests that organism density generally scales as a function of organism size to the power of -0.75 in aquatic systems. Thus, it seems that the ecosystem-level relation found here is a consequence of the organisational properties of the higher-level system and is not merely an echo of organism-level allometric phenomena. Such expansive regularity in pattern suggests the existence of fundamental rules governing the emergence, existence, and evolution of biological systems that are common to, but operate independently at, all levels of biological organisation.
Key words: allometry, scaling, metabolism, density
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.