Document: BRI-3-92-18

Energetic scaling of ontogenetic growth and allocation: Testing predictions of a general allometric model in vascular plants.

ENQUIST, B.J.* ^1,2, G.B.WEST ^2,3 and J.H.BROWN ^2,4

Univ. of California, Santa Barbara, USA ¹
The Santa Fe Institute, Santa Fe, NM USA ²
Los Alamos National Labs, Los Alamos, NM USA ³
Univ. of New Mexico, Albuquerque, NM 87131 USA ⁴

Abstract:
During ontogeny organisms typically show a sigmoidal pattern of growth in mass over time. Species, however, can differ in the time and size at which they attain reproductive maturity. Recently we have proposed a general model that is able account for the origin of quarter-power allometric scaling in both plants and animals. In particular the model predicts metabolic rate scaling as body mass, M , raised to the 3/4 exponent. Here we provide a theoretical extension of this model to mechanistically show how the constraints of allometry ramify to influence patterns of ontogenetic growth. Specifically, we derived a universal ontogenetic growth equation that shows how differences in allometric rates of cellular metabolism, cellular costs of maintenance, and allocation of production influence patterns of growth. Variation in the rate of physiological processing was shown to lead to predictable differences in the rate of biomass accumulation and maximum adult size. We tested these predictions for vascular plants using long-term growth rates as measured by tree rings and permanent plot monitoring. Observed growth trajectories were shown to be in excellent accordance with the model. Statistical fitting of ontogenetic growth trajectories was also shown to provide an alternative measure of rates of carbon assimilation. These results show that allometric rates of cellular processing and patterns of allocation ultimately limit the timing of reproductive maturity and biomass accumulation during ontogeny. More importantly, this work provides a mechanistic basis by which to develop a predictable framework for understanding the evolution of biological form and diversity.

Keywords: Scaling, allometry, allocation, ontogeny, growth, tree rings, dendrochronology.

This abstract is being presented at: 8:30 AM in session:
Oral Session #39: Theoretical Ecology.